Some potential benefit from atmos without more speakers
For home use the most interesting aspect of atmos might not be that it supports extra speakers, but that it can encode based on where sound should come from, not which speaker - re-mixing at playback time based on where the speakers are.
Given that many surround systems installed in a living room won't have ideal speaker placement this opens up the possibility of making better use of the speakers that are there with only a receiver change. This of course assumes that the receiver has some way to specify where you've put the speakers, rather than assuming they're in their nominal positions.