Since AP Mode was added in April to the MT7921 in mainline kernel, I was thinking of the following combination to use on the R64:
A 20 euro MT7921K NGFF version
With a 3 euro adapter.
The adapter does not have the 5V line connected to anything (pins 47 and 49 on mpcie), so that would make sure no 5 volts are send to the MT7921.
If the current drawn is too high (because of the limits on the R64 board), The 3.3V to the MT7921 is easily accessed at the two red circles. With the adapter removed, it would be easy to solder two wires and remove the copper traces of 3.3V on the mpcie side of the adapter. The 3.3 Volts can easily be taken from the 12V from the SATA power connector, in combination with a buck-converter to 3.3Volts. Could also just take 3.3V from GPIO connector, depending on what other hardware is connected.
What do you guys think?