In the lobby while waiting for the game to start, the host...can't remove players whom have accepted
You need to specify whether you're talking about players that you invited to the game or players that joined via open seats. The answer is very different between the two.
Sadly, I tend to get a lot of players whom cuss their mouths off, and hurl insults at every player in the game.
I don't think being able to remove people from the lobby would solve this. Most of the time I see, the bad behavior doesn't come from players until after the game starts, which renders your idea useless.
Instead, you should be reporting them. Click their name, then the Report button and they will be dealt with. You can also blacklist them so you won't see their chat anymore. This works both in the lobby and in the main game, which renders it superior to a method that only works in the lobby.
You should be adding your votes here: https://warlight.uservoice.com/forums/77051-warlight-features/suggestions/1080679-allow-game-host-to-remove-players-who-have-joined-