What's probably easier, an adaptor for PCI-E Atheros cards. PCI-E Atheros cards already exist for laptops.
PCI-express uses serial signalling at 2.5Gbps, with 8b10b coded data, with the clock information embedded with the data.
x1 cards (single data stream) which normally goes over copper/PCB backplanes, but could go on fibre
x1 PCI-E should be able to run on MM or SM fibre no problems, with a fibre transceiver each end connecting.
what's interesting, some people are looking at this already ...
What would be excellent about this solution is that it doesn't have any distortion or distance limitation, and electrical isolation makes the "downstairs" router proof from lightning strikes etc. Power for the "upstairs" PCI-E radio could be via a DC feed (24-48V) either separate or running in a hybrid cable with the fibre optics.