I have an idea that could make Teambuilder healthier and allow it to come back.

Make it similar to custom games selection with few changes:

-You can see few games displayed like the custom games, but on each game you can see what specification does the team leader want, how many people are on the lobby and what roles are taken.

-If the specifications suits you, you can enter the said game lobby, and then chose your role and your champion, runes, masteries and wait until the lobby is full, then launch the game after a "Ready/Not Ready" choice displays, like the old TB.

-The team leader could rename the lobby so it would be more appellant to players.

-Like the old Teambuilder, the leader select his owns specifications for the game (e.g. (for those who didn't know the original TB) what kind of champions(Marksman, Skirmisher, Warden) on what lane) but the leader can also change his specifications despite the lobby being visible (so waiting issues would be easily fixable).

I believe this could be a good way to improve the Teambuilder. I don't remember all the issues it had but I believe this concept would fix a lot of them. Also (I might be totally wrong but) it doesn't seem that hard to implement to me, since the custom games display is already there and I doubt that Riot entirely scraped the Teambuilder.