I don't know if this would work but here goes...
With the Mediator we can use PCI Realtek Ethernet cards. Into that we can connect a Wifi bridge to get wireless access. Is there any reason why this couldn't be combined in to one PCI card? So as far as the Amiga is concerned, the card is a standard Realtek RTL8139 Ethernet chipset, but then the card is internally connected to a Wifi Bridge with an antenna on the back of the PCI card.
I know there would not be enough of a market of Amiga users for this to be developed (if it would even work). But this could also be useful for people using Linux/Unix/BSD etc, as most kernels seem to support the RTL8139 chipset, so it would be much more compatible than Wifi chipsets.
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moto