Yeah I think it makes sense, I had similar thoughts. Currently the UI is assigning hosts to their final hostgroups in which they are being built later (because build flag is false). With pre-building we need extra association to keep track of the final hostgroup-assignment because the hosts would be assigned in the pre-building hostgroup. There may be other issues/complications I am not aware of. I would like to get this simple way working first than look at the possible optimizations.