GPIO breakout question

[pinus_pinea]

Hello, gonna front-load this with an apology for my utter newbness, and probably a whole slew of subsequent dumb questions.

I have a thought and I would like to ask if this is something that is possible. I was thinking about how one could go about getting access to, or expanding, the GPIO resources for the Pinebook Pro. In my searching around for existing info, I found the following: 

https://forum.pine64.org/showthread.php?tid=4785

I'm not so enthusiastic about doing everything through the SD card slot like that, but I def appreciate that that user was able to really probe the system for that functionality like that. 

I had another thought: is it possible to create some kind of add-on board/card using the PCIe x4 connection, some kind of bridge chip, and possibly some kind of MCU or other supporting ICs, that one could install through the M.2 connection, and then create a port physically somewhere on the case (I'm actually thinking of somehow machining the aluminum bottom case somehow to do this but whole other can of worms)? A whole "GPIO board" mounted on that connection using that bus? 

Is that dumb? Crazy amount of work? I'm not even sure where to start, mostly just wanted a lot more GPIO/physical computing ability for this platform.

[brken]

I had another thought: is it possible to create some kind of add-on board/card using the PCIe x4 connection, some kind of bridge chip, and possibly some kind of MCU or other supporting ICs, that one could install through the M.2 connection, and then create a port physically somewhere on the case (I'm actually thinking of somehow machining the aluminum bottom case somehow to do this but whole other can of worms)? A whole "GPIO board" mounted on that connection using that bus? 

Yes, it's possible. PCIe/UART bridges exist, but I suggest starting with an internal USB hub and a USB to UART bridge. I'd recommend modifying the below project to hold a USB/UART bridge, then manually running the USB connection from the test points on the board. I'm not an EE, but I believe you should be able to drop the UART bridge project's component set into the PBP WiFi project in KiCad. Then, with some layout and routing, you should be good to go

https://github.com/TobleMiner/PBP-NGFF-A-E-adapter

https://github.com/jiegec/HT42B534USB2UART (any other project like this should work but this one is just what i plucked off google)