I've wanted to make something like this too. After years of iteration, my self hosted setup is now completely automated and the automation itself is super simple and organized. It would be pretty simple to setup a simple web app that allows users to simply apply the same automation steps onto their own VPSs. Hardest part would be setting up a secure process for managing user secrets to be honest.

Business wise, I'm not sure I'd be willing to pay for just the automation... in reality you don't use it very often. Could be interesting to try (re)selling tightly knit VPSs, more advanced automation features or support.

I think this solution still captures the self hosted ideology while also providing some cool value. I see people reinventing the wheel all the time while trying to automate self hosted processes... but then again maybe that's why we do it, we like the adventure!