[Other Factions, more block types, weapons]

Quite simply like reassembly other factions with their own unique type of block shapes and weapons etc adds so much diversity and flavour to the game.

but if factions are not your game then just more block shapes would be cool

[Extra Game modes - Raids, Assault etc]

Currently i feel the current set of planet based missions lack variety. The inhibitors (slow down mechanic) can also be tedious and frustrating.

You could have non planet missions. With a play style similar to Reassembly you could just for example have a mission type called "Assault" that  has the objective where your drone has to destroy a mini fleet of drones a certain design or style. I think there would be a need for a block limit.

Another mission type could be Assassinate where you have to destroy one large complicated drone. Also a block limit would be needed.

Raids could be a planet mission where you have to mine a certain amount of ore from a very heavily defended planet

[SUMO Leader boards]

Leader boards for most overall sumo wins and designs with the most wins i feel would add more competitive interest to the game. 

I would also really love to see the sumo stats of each design, as well as my profiles overall sumo stats.  It really is satisfying winning a tournament and i would dig it if there was some expansion of tournaments or sumo in general.