here we go.
of course kata has standup grappling principles, there is no way to fight that close without it. but if you are suggesting full-blown ground grappling, you are coo-coo for cocoa puffs.
here's how we can logically analyze this:
Q: is there a significant portion of kata which has more than 2 points of contact to the floor?
Q: In order to train grappling effectively, is it better to train standing up and just imagine that it will work on the ground too...OR....actually train grappling in all ranges?
Q: do grapplers shadowbox? and if they do, is it while keeping minimum contact with the floor?
Q: are the physics of weight distribution/leverage/balance, etc different between standing and ground grappling?
Q: who are the best grapplers in the world? what are their training methods?
Q: did okinawans typically learn to grapple before or after gaining proficiency in forms? If you need grappling as a prerequisite to understand the forms, why use the forms for grappling? if forms were/are a training method to learn grappling, how come grapplers don't use forms?
* kata has standup grappling and clinch, I'd even buy standup submission.
* kata has ground grappling?
the physics seem fundamentally different due to the center of gravity shifts from the multiple points of contact to the floor. there is no way those lessons can be learned from 2-point-contact-to-the-floor kata. a simple example, a release from a headlock while standing is 180 degrees different than escaping a headlock while kneeling or sitting or laying down.