Assuming you were able to get the maximum capacity (you don't for a variety of reasons), the maximum capacity of a given access point is 1.2 gigabit/s. On a 2:1 ratio, that's about 800 megs down and 400 megs up.
Here is a graph of traffic from approx 200 GPON customers, with a mix of 200/200 and 1000/1000 subscription types:
Something tells me that would also work just fine with wireless operating at link speed of 1,2 Gbps. You would of course not be able to do 1000 Mbps upload with a link of 400 up, but you would be able to sell 200/200 no problem. The limit would be downstream capacity, not upstream.
Regards,
Baldur