I wouldn't mind a ultimate Combiner. It's name would be Omega Clusterfawk. Just imagine FIVE combiner teams that would combine into a giant robot. Each of these combiner teams are composed of FIVE members each.
All teams are composed of five vehicles that can change into individual robots.
Team A would be composed of a Tank team. All five are bots that change into various (cybertronian/organic) tanks. Everyone then combine into either a giant tank OR a giant robot. They would all combine to form the Omega Torso.
Team B would be a Car team. Combine into a giant truck or the Omega Left Arm.
Team C would be a Plane/copter team. Combine into a giant spaceship or the Omega Right Leg.
Team D would be various Dinosaurs. Combine into a Godzilla or the Omega Left Leg.
Finally, Team E are various regular animals. Combine into a Chimera or the Omega Right Arm.
All these teams them combine into Omega Clusterfawk. Of course, everything would be engeheerd so that all combined forms are perfectly ballanced, solid, and posable.