I would love this for Amiga! I am enjoying the WiModem for C64 and BBSs on the Amiga would be fantastic, given the faster speed, 80 columns, etc.
1) the c-64 wifi modem should have had a 6551 for reasonable transfer rates and plugged to the cartridge port
2) the amiga wifi modem should look like a plipbox and connect to the parallel port
I know they are just your opinions, so that's cool. But there are a few cons to doing it the way you suggest. 1. There are not that many terminal packages on the C64 that work with the cartridge port serial adapters. I think like 2 or so. Just about any terminal works with User Port versions. Personally I would rather have choice of terminals vs speed. At 2400 baud it is fine for BBSs on the C64, IMHO. In addition it does support the UP9600 hack.
2. I seem to recall, but I could be wrong, that the same is true of the Amiga. Most of the terminals that I used worked with the serial device modems.
This is a great device for it's intended purpose and makes it dead simple to connect to BBSs and telnet servers. And for the price it is an excellent deal.