I think gp is saying that since it switch from mono to core before you will be able to finish a game, you might have a bad time when they switch implementations.
It's certainly possible that that's the case, but I've seen a lot of projects go from Mono to .NET Core without much of a hiccup, too.
Probably worth pricing in some slack time to deal with it if it's a problem, but I struggle to think of changes from Mono to .NET Core which would be threatening to the ability to finish a project.
