Belts rankings above 5th have always been politicized. Always. When the degree system was being formed, Japanese martial artists collectively uprated their ranks to conform with a 10-rank system (previously, many arts stopped at 5th). James Mitose got a 10th dan in Aikido for promising to raise money for the Aikikai.
Then you have systems that award belts casually because the belts don't realy matter when it comes to authority or lineage. Bujinkan rankings used to be notorious for being handed out in a whimsical fashion and Hatsumi eventually rejected the 10th degree ceiling anyway, but this doesn't matter because inheriting the Bujinkan arts will happen completely outside of the system.
If you found your own art based on the 10-dan+kyu structure, though, you're stuck with occupying the 10th degree slot, because the idea that someone can exceed the founder is not generally accepted. I would think, however, that it would be a better idea to claim godan and let the second generation of your art award higher ranks, assuming it was your business to establish a new art in the first place.
Then you have systems that award belts casually because the belts don't realy matter when it comes to authority or lineage. Bujinkan rankings used to be notorious for being handed out in a whimsical fashion and Hatsumi eventually rejected the 10th degree ceiling anyway, but this doesn't matter because inheriting the Bujinkan arts will happen completely outside of the system.
If you found your own art based on the 10-dan+kyu structure, though, you're stuck with occupying the 10th degree slot, because the idea that someone can exceed the founder is not generally accepted. I would think, however, that it would be a better idea to claim godan and let the second generation of your art award higher ranks, assuming it was your business to establish a new art in the first place.