I've built a similar system, around 5 year ago. Users were able to deploy any version to any cluster from a nice UI. Basically you could select any version, click "Install" button and follow the logs in real time.

Behind the scenes it was a decentralized continuous delivery system. Very cool stuff, highly automated. Reduced a lot of work and sped up development cycles from months to minutes. Served quite a large software development organization (1000+). I think we had 1000 servers in 5 datacenters around the globe.

Nowdays I'm working on an open source version of that system, it's still missing few critical features but hopefully I'll get the first release out next spring.

btw, I'm looking for projects/contacts that would be interested in trying out how the system would fit their needs.