From my perspective, we are taking away less freedom for players by putting a limit to any room.
The purpose of training room was for people to train. But slowly, it has evolved into a room where people can relax and hangout with friends without spamming the lobby but also having the ability to be in character and chill.
I believe there will be another solution to more variety rooms if the player counts went up. Maybe adding some odd Tags like [R][IA] would bring some variety.
Then you would possiblity have a :
TDM Garden with [R][IA]
TDM Garden with no tags
AnD Mansion with [R][IA]
AnD Mansion with no tags
Some people enjoy the tags and play in those rooms. Some people don't like tags and play in the rooms without tags.