It would probably be "addition by subtraction", yes. If it were to be done, it would be for the purposes of television.
This is not to say that the programs themselves are a drag competitively, but now that Hockey East has its own national TV contract with NBCSN, it will be something to consider in the future. And the "elephant in the room" problem TV wise is that Hockey East has six of its current ten in the Boston DMA. Notre Dame will add a small home market, but presence in New York and Chicago (there's no doubt in my mind Notre Dame will be trying to leverage its 'subway alumni' for hockey, which is why NBCSN is fairly interested in ND hockey in the first place), and should UConn join, they add the 'best available' DMA to the HEA portfolio (Hartford-New Haven, in the top 30; HEA's current next best is Providence-New Bedford, somewhere in the 50-55 range).
With that amount of redundancy, Hockey East could probably secure a similar contract with fewer teams. Merrimack, Northeastern and UML could probably be dropped with no significant loss to the league's presence in the Boston DMA. UMA only brings Springfield with it, which is a market outside the top 100 (and made somewhat redundant being sandwiched between Boston and Hartford, DMA-wise). Hypothetically, were those four to be "left behind" from an Eastern NCHC, the per-team revenue share for that league would probably go up even if the contract itself stayed the same.
Now, if the line holds true thus far, and college hockey does not make for a significant source of ratings (read: advertising revenue), then such a possibility would be moot; if the overall contract is ****, then it doesn't matter if the per-team share is too low, because it won't be a measurable source of revenue for the teams. But I would think the "big players" in Hockey East would be foolish not to have such a plan in their back pocket.