IMO, it's more about conferences than Title IX.
Bear with me here. Title IX dictates (IIRC) that equal opportunities are for both sexes. So if one fields a college hockey team for men, one could satisfy the Title IX requirement by fielding a women's softball team, for example. Please correct me if I am wrong on this, as it is a main component for the rest of my post.
So, let's say Penn St decides to go D1 in hockey. Where do they go for a conference? If you follow the dollar (a big belief of mine and many others in the sports world), that would be the start of the cliched/forboden/etc BTHC. That is one team closer to that formation, and resulting in some mid-level teams (SCSU, MSU-M, etc) possibly eventually folding.
In other words, the threshold isn't how many more teams, it's how many more teams, where they ended up, and would added teams eventually result in the shrinking of the college hockey world. We would have subtraction by addition in the west, whch is about 50% of the college hockey world (in money/fame) as we know it.
If one could get the club teams (from what I have learned through here is mostly midwest) to have their own conference, than I'd say the total team threshold resides around 70, yes. If those teams result in a push for conference realignment........I think that threshold DROPS to 50 or so. Best case, in a few years, to allow for dwindling attendance/$$$ until schools finally give up on their programs.