I would be extremely surprised if this isn't on the list of things to do already, but I'll put it here anyway on the offchance that it's not.
I feel like it's a bit excessive and annoying to have to restart the game if you want to join a different server or go into single-player from a server. It'd make much more sense to have a similar system to Minecraft, where you can leave a server and go into single-player, go from single-player to multiplayer and switch between different servers without restarting. Of course, I know it's probably low-priority, and will not be added for a while.
Another thing I'm thinking of, which I suspect is also already on the list of things to add, is multiple single-player worlds. Again, I'm thinking of a similar system to Minecraft.
I feel like it's a bit excessive and annoying to have to restart the game if you want to join a different server or go into single-player from a server. It'd make much more sense to have a similar system to Minecraft, where you can leave a server and go into single-player, go from single-player to multiplayer and switch between different servers without restarting. Of course, I know it's probably low-priority, and will not be added for a while.
Another thing I'm thinking of, which I suspect is also already on the list of things to add, is multiple single-player worlds. Again, I'm thinking of a similar system to Minecraft.