I'd be less interested in a beefier SoC. A64 isn't top of the line and it could do with a die shrink for better power consumption, but the performance is sufficient for doing what a phone is supposed to do.
Here's what I'd look into for the next iteration:
1. Better antennas
2. Bigger battery and/or secondary battery
3. Better microphone routing
4. Better call speaker
5. Better media speaker(s)
6. Maybe more RAM
Reasoning:
1. Due to social distancing I'm currently at a remote location where I know reception is bad, so it's the perfect testing grounds for cell reception. So far the PinePhone is struggling to perform at all on GSM (2G). I haven't tested HSPA (3G) a lot but it seems to be more or less a lost cause, cell reception is bad when it works at all, although I know we have particularly bad HSPA here.
LTE on the other hand performs reasonably well. It's not like my other phones but it's good enough to works with. LTE has the best cell coverage here by far, even though it shares bands with GSM. My guess is that the cell tower is doing something odd. I'm hoping we can enable the VoLTE capabilities of the EG25-G soon so that I can have good reception again.
2. This is in the works of being solved for the current iteration by means of making the battery thicker. I'd say we can go way thicker for the odd use cases, but since the battery doesn't have the same shape as the frame it would either look weird or not use the internal space very efficiently. I'm fine with it looking weird (and having another edge on the back to hold on to with the pinkie would be awesome) but I would investigate using a second battery with a different shape (larger area) that sits in top of the first battery when you take the back cover off.
That way you can hot swap it with another battery and you can use an external charger with cooling to prolong the life of the secondary batteries. This also enables us to run the primary battery at lower apparent capacity, keeping it in the 20-80% charge level range. This should significantly increase the life span of the primary battery and in emergencies you could activate those last 20% to make a 911/112/999/119 call. We could even keep the J7 battery (using a common battery was a great idea) and use another common battery for the secondary. This has the added benefit that when the J7 battery eventually ceases production we could still get off the shelves batteries for the secondary to keep the phones alive while we find another model for the primary (or vice versa if we're unlucky with the secondary).
As far as I know this concept hasn't really been tried on any other consumer device than business targeted laptops. There was a phone with a really small battery just for hot swapping but you couldn't use it that way. With the pogo pins this could probably be implemented on the current PinePhone.
3. From what I've heard from others there's a lot of radio interference on the microphone. Fixing this could be as easy as using a slightly different ribbon cable design or require more extensive work on the bottom board. Microphones are hard to get right and especially so with long analog signal paths.
4. The call speaker lacks clarity and amplitude. A lot of it could be mitigated in software with some equalization, but the better the hardware the better the end result. If we decide to use dual front speakers in the future we could just use one of those and bump the amplitude way up together with the frequency response. This also leaves a lot of headroom for equalization.
5. This ties in with the previous point; one front facing speaker at each end of the front would improve sound a lot. Rear facing speakers are hard to get right because you need to work with reflections to get decent amplitude and frequency response.
6. 2GB is plenty for normal use and there's always swap to cover edge cases but more RAM seems to be frequently requested and would come in handy when convergence starts working properly.
As you can see there's plenty of cool things to be done without changing the SoC. Sometimes it's the things you don't see on the spec sheet that makes a phone good.
Edit: I forgot to say I like your idea of a secondary USB port (which is something the Pyra Handheld will have). I don't know how we would fit it on there or even interface it with the A64 but it's still a good idea.
Here's what I'd look into for the next iteration:
1. Better antennas
2. Bigger battery and/or secondary battery
3. Better microphone routing
4. Better call speaker
5. Better media speaker(s)
6. Maybe more RAM
Reasoning:
1. Due to social distancing I'm currently at a remote location where I know reception is bad, so it's the perfect testing grounds for cell reception. So far the PinePhone is struggling to perform at all on GSM (2G). I haven't tested HSPA (3G) a lot but it seems to be more or less a lost cause, cell reception is bad when it works at all, although I know we have particularly bad HSPA here.
LTE on the other hand performs reasonably well. It's not like my other phones but it's good enough to works with. LTE has the best cell coverage here by far, even though it shares bands with GSM. My guess is that the cell tower is doing something odd. I'm hoping we can enable the VoLTE capabilities of the EG25-G soon so that I can have good reception again.
2. This is in the works of being solved for the current iteration by means of making the battery thicker. I'd say we can go way thicker for the odd use cases, but since the battery doesn't have the same shape as the frame it would either look weird or not use the internal space very efficiently. I'm fine with it looking weird (and having another edge on the back to hold on to with the pinkie would be awesome) but I would investigate using a second battery with a different shape (larger area) that sits in top of the first battery when you take the back cover off.
That way you can hot swap it with another battery and you can use an external charger with cooling to prolong the life of the secondary batteries. This also enables us to run the primary battery at lower apparent capacity, keeping it in the 20-80% charge level range. This should significantly increase the life span of the primary battery and in emergencies you could activate those last 20% to make a 911/112/999/119 call. We could even keep the J7 battery (using a common battery was a great idea) and use another common battery for the secondary. This has the added benefit that when the J7 battery eventually ceases production we could still get off the shelves batteries for the secondary to keep the phones alive while we find another model for the primary (or vice versa if we're unlucky with the secondary).
As far as I know this concept hasn't really been tried on any other consumer device than business targeted laptops. There was a phone with a really small battery just for hot swapping but you couldn't use it that way. With the pogo pins this could probably be implemented on the current PinePhone.
3. From what I've heard from others there's a lot of radio interference on the microphone. Fixing this could be as easy as using a slightly different ribbon cable design or require more extensive work on the bottom board. Microphones are hard to get right and especially so with long analog signal paths.
4. The call speaker lacks clarity and amplitude. A lot of it could be mitigated in software with some equalization, but the better the hardware the better the end result. If we decide to use dual front speakers in the future we could just use one of those and bump the amplitude way up together with the frequency response. This also leaves a lot of headroom for equalization.
5. This ties in with the previous point; one front facing speaker at each end of the front would improve sound a lot. Rear facing speakers are hard to get right because you need to work with reflections to get decent amplitude and frequency response.
6. 2GB is plenty for normal use and there's always swap to cover edge cases but more RAM seems to be frequently requested and would come in handy when convergence starts working properly.
As you can see there's plenty of cool things to be done without changing the SoC. Sometimes it's the things you don't see on the spec sheet that makes a phone good.
Edit: I forgot to say I like your idea of a secondary USB port (which is something the Pyra Handheld will have). I don't know how we would fit it on there or even interface it with the A64 but it's still a good idea.