Well... I say don't add anything other than more controls for in lobby use and extra players, colors, and maps. I'd save any super Changes for a Squeal.
I would save a friend system for AU2, new roles for AU2, and more Expansive maps for AU2. The only thing I'd work towards in AU1 is Server stability, being able to change all Gameplay options in Lobby, maybe add map limits so round balance is stable(the skeld and Mira HQ can't handle the current limits as is so those need to be locked or maps need to be rescaled), and I'd use the stabilization/expansion process of AU1 be the groundwork for the Engine of AU2. I'd make the joke this is the AU1 remake process.
You guys have released an awesome game and with the influx of cash I'd do the overhaul to make the game stronger and save any major changes for the Squeal just so the original game isn't lost.