>>8377043Good question! It seems to me like Hasbro mainly tends to reuse relatively recent molds, so that would limit things considerably since about half the molds from the past few years have been bogged down by line-wide gimmicks (headmasters, combination, etc).
If we're assuming we're stuck with that limitation, and I absolutely HAD to use nothing but recent molds from the last five or so years, and just completely ignored the obtrusive gimmicks some of them have, it would probably be this:
Autobots:
Optimus Prime - TR Voyager Prime (using Octane remolded chest)
Sandstorm - Generations Selects Rotorstorm
Prowl - Siege Mirage
Mirage - Keep the Botcon version
Hoist - Keep the Botcon version
Hubcap - Siege Hound maybe?
Decepticons:
Megtron & Megaplex - My first instinct is to say TR Triggerhappy, buy you know who might be a surprisingly fun pick? Siege Flywheels/Skytread! He's got the cockpit chest, and the lower half being a tank might be a fun Megatron throwback. ...Dang, I actually kinda want to see that now.
Starscream - Is Siege Jetfire too much to ask? If that's not an option, maybe settle for TR Sky Shadow since I feel like he should be a big guy.
Soundwave - Everyone's obvious choice would be Earthrise Doubledealer, but I don't have it yet to give my firsthand opinion, so TR Hardhead/Quake should be on standby if DD ends up being bland.
Skywarp & Thundercracker - Would the Earthrise seekers be too obvious of a choice? Give it a new headsculpt and it could work. But honestly, another option I think would be really great is CW Fireflight. He lacks the cockpit-chest, but his simple transformation would be great as an update for flip-changers. Heck, swap Starscream's mold for Silverbolt, and change Megatron & Megaplex to CW Skydive, and you've have a whole combiner team, plus Soundwave just chillin' nearby (unless you tried to give him a CW mold too, like Rook or something, but I'm not sure if any of them fit him well enough).