Yeah tbh why not use just that idea from Omnitrixx?? With time/universe traveling etc. they could fulfill basically every wish of everyone in that poll.
They could use a fresh new character who has the power to cross the universes & time & has to save the universe by seeding all those characters in all those universes. Pick a few main chars + some favorite side chars of all the shows & boom.
They could even experiment with many different artstyles due to the differences of those shows.
That way they don't have to force themselves to use a show that no one is interested in to see. They could even use some obscure TLA characters who were ever known by name or never appeared at all.
I may be biased cuz I love Ben 10 but I legit think they could pull it off, as long as they develop a roadmap and split each universe into separate "Books" like with FET.
Or keep the main focus in the Ben 10 universe, and go through these different universes now and then to fight off the Big Bad/find some "infinity stone" type plot device in each world for it. Could legit do the "Shady" thing too lol and make the villain the evil alternate timeline Ben.
And harem ending even easier cuz sci-fi bs lol
Hell, Ben even canonically visits other universes.
Would love to see babes from Generator Rex/Secret Saturdays as well.
Seems like the best big project solution but I guess they have other plans.