Is there any way to edit room descriptions in ships/etc right now? After the sync.

No

Been told it was planned for a later sync, along with room images and other things.

Does that mean the custom descriptions have been deleted? Or just 'blocked' from being seen?

I should think they're just not in the interface. I think people will be rather upset if they're completely gone.

That's relief, had a cool description for the entrance to mah YT (where unwanted visitors were greeted with a threat about being forcefed the hull if they didn't announce their intentions, even included the embedded tooth of a previous intruder :D)