Carriers are coming, Marine/paratroopers are highly debated.
Two research slots are fine, it means you have to balance your research and development. Part of being a Commander is figuring what matters more. If you want nukes, but everyone else in the game is pulling away with LvL 4 Medium tanks and you only have Lvl 2, you need to use one of your two slots to sort that problem out.
Any more than two slots would mean spam researching, and that would shorten the games and strategic aspect of the game.
