OpenRA

Why not make the server list viable while you are in a server? Maybe show a number of how many people are in the main lobby so you know if you should wait around to get a game going or not?
A lot of people will leave a server just to check if there are any others that popped up with a lot of players.

These would be really nice, to say the least. Maybe have a lobby system where you can switch between the masterserver listings, the game you're in, and chatrooms/etc with tabs?

The UI is always going to change. It's one of the weakest areas of the game in both code and design.
I or someone else will eventually implement an IRC-backed lobby system for chatting and the like.
See https://github.com/OpenRA/OpenRA/issues/2088 for any developments