I think we need to distinguish between getting a service up and running and maintaining/securing it. Because yes, getting up and running is doable. *Staying* up and running, maybe less so.
Plenty of services exist to do what you're saying. Understanding the tech debt and security tradeoffs of them does not come easily. Sorry, no two ways about that.
You want to make a tool that automates the hard parts? Great! You want to have that deploy VPSes for people? Great! Such tools do exist, but guess what: you've made IaaS or SaaS.
Also, FWIW, there is nothing whatsoever "sustainable" about everyone having their own VPS. I would contend that that isn't even self-hosting in the sense that matters for this conversation. While I too use cloud VMs as reverse proxies, I recognize that doing so is a liability I accept to keep attackers off my home IP. And I do so knowing how to maintain and secure the machine. I could also pay a service to do so for me, but then we're back at the original problem.