It would be able to handle it. So would 3G. I've used Facetime on a WiFi connection that only had a 3 Mbps throughput and it was fine - no choppiness at all. I think that the main reason 3G access is turned off in Facetime by Apple is that the carriers (mainly U.S.) don't want it to overload their networks.^ I know that but I figured the reason it was only on wifi presently was because '3G' wasn't fast enough to support it.
How do we know true '4G' won't be able to handle it?