I'd like to see Ratbat, since Galvatron has been waaaaaay overused since RID/Unicron trilogy made it standard for Megatron to upgrade to Galvatron in every series. Also, Car Wash of Doom ftw.
Id really rather a Ratbat/Porter.c.Powell team up but then there seems to be this oddity where everyone wants one human villain or another becoming a TF which in and of itself I think is an awesome concept but one I think would be better handled with a villain created for that purpose turning into a 'New' bot like Lugnut, Bulkhead and Lockdown than a homage bot.
Just make it a carwash that's been affected by an Allspark shard and makes the Autobots go nuts when they go for a wash and it would be perfect for an Animated episode.
I think I would like Galvatron as a separate character. Because we all know that the whole Megatron-upgrades to Galvatron thing, and I think that due to the whole Animated taking on a different pace, I think that's what they're doing.