I'm tempted to just start with CW Optimus being repainted into SG Optimus. However, SG OP has already gotten 2 releases. I figured we try another tack - one with potentially interesting story results. Repaint CW OP into SG Ultra Magnus. Give him a new, skull-like bot mode head, paint his windows purple like he had in the comic and give him a translucent purple version of Motormaster's sword to be the Terminus Blade. Have the combined mode be Optimus himself! The two inimical brothers now share a body...
SG Ironhide from CW Ironhide seems like a no brainier. It would be better than using the universe mold (as his character model does), but it would mean using the Off-Road mold in black a second time after Trailbreaker. Maybe stick the Ironhide head onto the First Aid body instead?
A new SG Wheeljack wouldn't be bad either; obviously it would use the upcoming CW Wheeljack remold of Breakdown. What's pretty neat is that it would mean that both SG Wheeljacks were different kinds of combiner!
Repaint Air Raid into SG Jetfire. The air Raid mold looks a fair bit like the Classics Jetfire mold, and probably wouldn't need a new head.
For the last one, do SG Sunstreaker from his CW counterpart. Not a very compelling character, but it sets up a nice symmetry with one of the Decepticons (read on).
For the legends partner, repaint CW Hot Rod into a new character - SG Minimus Ambus! Have him be characterized as Magnus's slave that he won by defeating Dominus Ambus in combat. Or something.
Throw in a few more support team figures:
SG Prowl, simply because he hasn't gotten a toy yet, and legends SG Wreck-Gar from his CW toy (maybe in triplicate?)
So, for the decepticons:
SG Cyclonus from CW Cyclonus. Wait - are you saying you want the second combiner to be evil too?! Well, we all know that the Galvatronus torso has a strong Emperor Starscream resemblance. Have the story go like so: after Cyclonus "assassinates" Megatron, the newly in-command Starscream, who has recently discovered that his spark is indestructable, decides to possess Cyclonus as a combiner. This prevents Cyclonus, a very powerful asset, from defecting to the Autobots, and also allows Starscream to control Cyclonus's great power in combiner mode. He declares himself Lord Starscream, though intended in a benevolent manner.
His team members include Skywarp and Thundercracker, from Air Raid and Skydive respectively. They both share the same new head mold.
For a legends partner, we can finally get a SG Shockwave.
For support staff, use Breakdown with a new head to make SG Sideswipe.
On the Beast Wars end of things, 2016 is the 20th anniversary of that era of the franchise and while we got some pretty cool stuff for the 10th anniversary, it seems like the only 20th anniversary items are the red/blue repaint of the giant BM Primal toy that was originally released during RiD and FP's Botcon set with its take on Tripredacus. However, I would really have liked to see a normal retail release of BW combiners, one for each faction and using the main characters. Since some of these characters are showing up in the IDW books anyway on a colony planet, have it be those versions of them or make a new time line where it's the BW cast that lands on Earth instead of the G1 guys.
Cheetor from Dragstrip
Rhinox from First Aid
Tigatron from Dead End
Dinobot from Swindle
Rattrap from Blackjack
Airrazor from Powerglide
Primal from Optimus Prime
Combined mode: Optimal Optimus
Waspinator from Vortex
Terrorsaur from Sky Dive
Scorponok from Rook
Inferno from Brawl
Tarantulus from Shockwave
Blackarachnia from Groove
Megatron from Onslaught
Everyone would get new heads!
I toyed with having both Cheetor and Tigatron being straight repaints of Prowl, and I still wouldn't mind Prowl's head being used, but I thought that the alt modes of Drag Strip and Dead End evoked Cheetor and Tigatron's alt modes better than Prowl's (as much as I love Prowl's car mode). Rhinox could have been the voyager core, since he's bigger than the other S1 Maximals, but I decided to go with First Aid, again largely because I think his "ambulance" mode is a pretty decent rhino equivalent. Dinobot was kind of the toughest, largely because no one has ever really pinned down what is vehicle mode "should" be. His weapon suggests helicopter, but the Alpha Bravo mode doesn't allow the rotors go be used as a bot mode weapon. I also didn't think a tank or APC was appropriate enough, since a raptor is one of the less heavy carnosaurs. I settled on the Swindle reshell of Rook as the best choice, partly because of the alt mode and partly because I think someo of the bot mode details on the chest and shins evoke the bones Dinobot sports. Primal from Prime is almost too easy, to the point that I was close to choosing something else, but it just works too well. I'm honestly not settled on Optimal Optimus as the combined form, partly since I thought brand new characters for the combined modes might be cool since everyone else is a straight homage. That and I think The Optimal head design is fine, but I think it might look weird in the blue/Orange atop a mostly black body. We'll see. Rattrap could have easily used the Groove mold as a DOFP homage, but the Blackjack mold works with the Optimus mold, so that's easier.
I've always thought that a helicopter would be a great vehicle to go with Waspinator, despite "Possession," the TM toy, DOFP and the overall temptation to make him a latter-day Seeker. Sky Dive is too easy as Terrorsaur. For Scorponok, I know FP is using Rook for Tarantulus, but I think it works better for a scorpion with the claw weapon and potential to give him "claws" in the form of combiner hands. The claw weapon could even be interpreted as a "tail" in alt mode. I picked Brawl for Inferno since he's an army ant, and few vehicles say "army" like a tank.
One more idea: BM Vehicon Combiner!
Torso: Jetstorm from Cyclonus (new head)
Combined mode: Megatron (new helmeted head instead of Galvatronus)
Tankor from Brawl
Obsidian from Alpha
Thrust from Afterburner
Strika from Rook
Diagnostic Drone from Shockwave