You can already do this with MySQL/Postgres/etc., and there's no special magic in any of these newer tools that allow you to avoid the speed of light. The reason people don't typically run WAN synchronous setups is exactly because of that (and network reliability).

The only way to a "free lunch" is via CRDTs.

edit: This is in no way a knock on FDB by the way. I think it's a really interesting piece of technology and I want to explore it more. Just that it doesn't have a way to do consensus faster than the speed of light :)