Huh, I thought I'd replied to this already. Anyway, while I had mainly envisioned it requiring the features be attached to a solid object, given the level it's gained and what you can already do with features, I don't think it would be particularly broken or otherwise problematic if they could be placed on things like clouds or just floating in the air. I'd say that as written they can be, but the final call is up to the DM.
I see. Not having played pathfinder, I can't say what a decent conversion method would be either. I may try looking into it though if I get the chance.
Owrtho