The notes on the front page say the tier 2 fleet research unlocks it now, which seems like a weird place for it.
It's also strange that they're more expensive in CO than battle cruisers. I was hoping to deploy some defensive orbitals using the new conversion mechanism, but they're twice as expensive as the orbital, which seems pretty steep! :-)

I haven't researched any fleet tech yet, so I guess it'll be a while before I can test if Forward Fleet does in fact unlock cruisers. It has no mention of it in the game tooltip.