I would really love to see Rated Frysk!, Russian, Brazilian and Frisian UltraBullet here

If we had more players perhaps, but you are always free to create your own tournaments within those time controls. I know I would jion.

Realistically what would happen first is that variant would be split into 3+0 or shorter and 3+1 or longer. We can see though on lichess the variant there has 50x as many players and they have not broken theirs down.

Yeah, ultrabullet is a lot of fun, also for other variants in my opinion. On the other hand, more broadwise, a lot less players are interested in ultrabullet and besides this, there is something else very important to be aware off: The other variants have just one rating, no different ratingcategories for each timecontrol (bullet, blitz, rapid etc.). So ultrabullet tournaments for those variants will way to much influence the rating of that variant, the reached rating will less mean something about the playing strength. This is why ultrabullet is not scheduled in regular tournaments for variants (likewise with hyperbullet).

But as Bobkingmen3 said, everyone is free to create their own ultrabullet tournaments ;)