You can join room 2 and right click to spectate room 1. Chat and player count changes in room 2 will be visible ingame, so you can keep track of it to switch to the lobby.
You could try the propose system
https://zero-k.info/mediawiki/Setting_Up_a_Game#Propose_BattleAt 56 players, then the !split command will work too.
The central issue is of how to create a system that players trust to not cause them to miss out on games. If you go sit in another room, then a game could start in the main room, and you'll miss it. The quality of the game matters too. Maybe you get a 4v4 of high skill variance instead of a spot in the next 16v16. Maybe the room evaporates after the 4v4 because someone leaves and nobody wants to start a 3v4. Smaller rooms are at a higher risk of evaporating suddenly.
I don't think any significant number of players are going to follow a text prompt to join the other lobby. And then when too few players join for it to be worthwhile, the number of players following the prompt will drop to zero. Similar, more automated, questions have been tried.
Something that automatically sends you to the other lobby when you rejoin to spectate the game could be created, but it risks doing things against player preferences. It is a coordination problem where the first mover is disadvantaged. People can only be moved when they are going to get a better outcome than by staying put.
