Cruisers are already in, they are just clumped with frigates. It's mostly an engine classification, really a frigate can be any ship. Those missile platforms the Sova deploys, and siege platforms from Vulkoras - those are "frigate" types, too.
It's a classification so the engine knows how to treat the entity. Frigate types can be assigned to the frigate factory, while Capital types go to the capital ship factory. Capital types can have levels, Frigate types can't - things like that.
