Vex has useful normal gears.
Vex has more useful high strength gears (except for 84t).
Vex has educational gears like differential.
Vex has useful and educational bevel and worm gears.
(but not a HS worm wheel with metal axle hole).
A planetary gear would be the next logical step in the Vex family.
The Ring gear would need to have 60t or 84t on the outside to mix well.
The Sun and or planet gears could be normal or HS 12t,
Or maybe a ~15t Sungear that works with 12t planets,
and a 12t sun gear that works with 15t planets.
One goal would be to make a compact gear down box for lever arms.
Another goal would be to make a compact speed up gear box for fast wheels.
A good idea would be in developing the ring gears, is that the outer edges of the gear should be made in such a way that it can be rotated and supported so the gear could become a durable platform for a crane or turret. (make a comment about this if it doesn’t make sense)
I think a ball-bearking turntable like this one would make a great addition to the Vex product line. But think how much more interesting and flexible it would be if they added a ring-gear inside the opening.
The ring-gear would be attached to one plate, but the other plate would be free-turning. That would allow you to mount it as a stationary outer-ring for a planetary gear box, or use it as a turret-mount that could be direct-driven or planetary-driven.
The last (and probably trickiest) part to design is the planet carrier…