for a little more planet variety, what would you think of a second parameter size, next to the existing one type?
what about 'small ice worlds', 'huge desert planets', 'big asteroids'? the sizes then also changes the underlying parameters, such as pop size, logistics space, tactical space and stuff. that way, we have a bit more variety with a fairly easy way and it probably can be balanced, so that players are not disadvantages vs one another. those types are then further diversified by all those bonuses that are already in the game, but at least there is an obvious, discernible variance that makes a feelable gameplay difference.
if not, maybe this idea can be implemented in one of the mods (at least I think it is not yet), because as I see it, there are a few out here that introduce several new types. hope they are at 1.11 soon.