Another stage is an interesting idea but I think there is no time to do it right now.
There is couple of problems for staypuft with approach of keeping it as Discovered host.
- We also need that the method works with already managed virtual machines which is very useful for testing.
- an user may want to see the usual full edit page for host before he triggers Deploy
- also manipulating with hostgroup_id without association feels to me hackish, using current foreman's tools (environment and template combinations) preconfigured by staypuft installer seems better to me.