Personally, I think 17-15 is as good as we'll get, especially given the history of the situation. Creating conferences and divisions isn't a path independent process; it matters how you get there. With Columbus and Detroit being the two teams most geographically fit to travel, and with them both having just breathed a collective sigh of relief after being relocated, there's not much that can be done. Going west, the next three teams look like Pittsburgh, Toronto, and Tampa Bay - none of those are happening.
Imbalance can work, and be fair. Let's assume Seattle and Portland - or any other team out west - isn't going to happen, but that QUE is happening. If you could get GTA2, the Whalers, and one other team in the East (Atlanta with competent management?), you'd have 20-15. Playoffs could be 8 teams from the East, 6 teams from the West, which is proportional. The Conference leaders get a first round bye. Other teams are seeded - no more "divisional rivalries". Bottom team in the East gets transferred to the West for the playoffs to play against their top non-bye seed.
Boston/Montreal SCF, anyone?
I'm not saying expansion has to happen, or is even a good idea - 35 teams is a bit of a pipe dream now, when no other league has more than 32. All that said, the current divisional setup has its advantages - namely, convenient TV scheduling, and the creation of rivalries. I like the idea of winning the Cup by going through MTL.