Hi! Welcome!
This is not a new idea :). There have been discussions in the past about Cinnamon remixes of Ubuntu, but nobody appears to have stepped up to do the work to make it happen. It would indeed be awesome to see a well maintained, up to date and beautiful cinnamon based remix of Ubuntu, I hope you can find some people to coalesce around the idea.
Note: I’m mentioning “remixes” rather than “flavours” because there’s a lot of work to do in order to become an official flavour of Ubuntu. You don’t get there without a lot of work. It’s best to start off as an “Ubuntu Cinnamon Remix” initially. But the name is the last thing to worry about 
In my mind the first step is to ensure the packages for cinnamon and whatever else is required are up to date in the Ubuntu archive. The best way to do that is make sure they’re well maintained in Debian first. It looks like in Debian and recent Ubuntu releases we have those packages, so that’s a great start.
I’d suggest a good next step is to take the lead and start learning how to build a custom ISO image, and get building. See what you can make yourself. Having something to build upon will make it more compelling for others to get involved.
Next is exactly what you’ve done, find people who are willing to work on the project. I’d recommend spreading this thread far and wide to find more people who might have the skills and time to get involved.