I gave it some thought, and I decided that ToV and EN should continue to have 7.1.5+ rankings in their own partition. Unlike previous expansions, people really are still running this older content quite a bit, for reasons ranging from farming for AP and legendaries, to trying to get gear from ToV that actually manages to be better than Nighthold gear.
We’ll see if the site can handle this in terms of performance. If it turns out to be too much of a strain to have two tiers open simultaneously, I will turn them off again.