With Prowl comes Bluestreak and Smokescreen. I have also read rumours of MP Constructicons and a Megatron version 2 to be in scale with the current releases.
More than rumour, these words come from established and reliable insiders.
Prowl is the next medium and Galvatron is the next large.
Keep in mind that TT has MANY MP CAD's ready to go so the order may change IF a 3P group forces Takara's hand.
If anyone hasn't noticed, Takara is agressively attacking 3P groups by finally catering MORE to fans vs general public.