Maybe if people you recently played with could show up in your recent players on steam, that would be great

That would be cool!

maybe a lobby or some chat function?

Yeah, Shiny_Bulbasaur you bring up a good point. I was playing with someone random the other day and was hoping I didn't have to screenshot his steam name to keep track of him and talk to him, maybe open a voice chat call so we could talk during play etc... and there wasn't anything in the overlay to do that. So these are good suggestions and we'll maybe look into seeing if we can't figure out how to integrate it- as it is a base Steamworks feature.

Another thing we'll be patching in hopefully soon is a fix that will make arcade mode players able to play against each other through random matchmaking if they both have "accept challengers" turned on. The way it would work is it would randomly auto-join the first game that loads in (so it auto-filters for best connection) every time you go back to the level select screen. This way if all the players join using arcade mode they'll keep joining and playing against each other almost constantly and when you're playing in an arcade mode map you should receive challenges sooner!