[Snowflakian]

I'd pick one of these 4.

Inhumanoids - using GI Joe 25th, RoC, PoC, and Retaliation figures for a large filler basis. Monsters would have more variety too. I'd also use this as an establishment point and expand to cross hasbro universes and unite them. In this case Renegades and a Transformers universe of some kind. I've gone on more about how I'd do this, and how I'd want to balance classic in the history before alongisde how I'd streamline the designs for the future too. So it could usher in new stories while still holding true to the past.

Centurions - Same as above and joe scale. But instead of Earthcorps, this would pretty much be skycorps. Again would stream line the designs in joe scale, and would balance it to still fit within the confines of the joined universe. Probably would even make this the after earthcorps tech and threat evolution, or even a side unit to GI Joe's subcontractors like Earthcorp, and so on. Pretty much I'd do this as a Prequel point to what the series became. How the tech was developed, how it evolved, and how the transporter and sky station came to be alongside the bad guy.

Exo-Squad/Robotech
I'd want to relaunch the toys at least, or new interpretations of their designs, but this time done in Megablok and compatible with Halo megabloks. This way the E-Frames, Jump Frames, Mechs, and other ships can also bolster the Halo armadas and vice versa.
I'd kill to have E-Frames MB spartans could use. Invid Shock Troopers and scouts would just be icing on the cake.

Bots Master
The concept was very 80s meets the future. It could really work now. Keep the spirit the same, but update the designs of everyone as needed. I'd also focus more on getting the expanded out and better transforming bad guys.
So stuff like twig and the car, and let them combine too into a robot for the toy. That always pissed me off on the original. Also done entirely in Joe scale of course.