I have to say this:

Is there a stigma or curse against using the canon riders? With the exception of 2 stories every kamen rider x precure has OC's.

Does every story needs to have a ship insted of just being friends or comrades?

This could be really interesting, I've been hoping for a Star twinkle/Kamen rider crossover

Kai Daiki? You got it wrong, mate. Kaito is his (Diend) family name. In western order, his name should be Daiki Kaito. Just look at the name of his brother from World of Diend, Junichi Kaito.