I agree, I would love having official full support as well.
Regarding PCIe performance: Nope, you will very likely not get that on Debian mainline ever. The reason is that setting this is not safe by default because some boards seem to be faulty as discussed in this thread: https://forum.pine64.org/showthread.php?tid=8374
However, this is "just" a matter of the DTB file and not the kernel itself. Therefore, you just need to patch the dts, compile it to obtain the "speedy" DTB once and put it "hard-wired" in your Debian system. At least this is my plan and it seems to work fine so far.
Regarding PCIe performance: Nope, you will very likely not get that on Debian mainline ever. The reason is that setting this is not safe by default because some boards seem to be faulty as discussed in this thread: https://forum.pine64.org/showthread.php?tid=8374
However, this is "just" a matter of the DTB file and not the kernel itself. Therefore, you just need to patch the dts, compile it to obtain the "speedy" DTB once and put it "hard-wired" in your Debian system. At least this is my plan and it seems to work fine so far.