What Themes have Kamen Rider not tried yet?

[Kero]

What Themes have Kamen Rider not tried yet?

[Green Elephant]

Sports.

I'm coming up with Kamen Rider MVP

A disgraced boxer finds the MVP Belt to fight the Mascoundrels (living mascots). His basic form is a boxer/soccer player. He also gets new forms from traitor Mascoundrels: the tiger gives him a baseball bat-like sword for Slugger Form (super speed), the hawk gives him a crossbow for Shooter Form (super senses) and the polar bear gives him a hockey stick for Slapper Form (super strength). Put them together for Triathalon Form

His ally has a suit based on golf and tennis.

Yes I like the Kiva Concept (that was the template)

[Kero]

Basically this is what I can list.

Frogs? I have one http://www.freewebs.com/kero2008/apps/photos/photo.jsp?photoID=27593465&prev=1
Fish?
Outer Space?
Cyberspace?
Spiders?
Ocean-based Riders?
Nanotechnology?

[SparrowRanger]

Heisei era's Kamen Rider series seems to be much more flexible than Sentai in terms of themes. It seems to me that Sentai just keeps on recycling (Animals & Vehicles, throw in a dash of mythical creatures every once in a while, rinse & repeat) which I think is because they want to make sure the series would be easy to 'Americanize' (That being said, Shinkenger looks like its going to be hell to localise).

To answer your question, there are unlimited possibilities (which are evident by all the fanfiction & fanart you'll see on the net). Your suggestions seem interesting though

[chaos]

ninjas
computer hardware
soft drinks
star trek
dragons
wizards
mmos
something like fate stay night were they summon mythical heros warriors ex

also i would expect a battle with giant robots and monsters to be a pain. Also this would probably cause your insurence to go through the roof and ruin the value of your legal residence