There's no guarantee that Michigan and Michigan State adding women's hockey would lead to it becoming a Big 10 conference sport. It would produce a significant increase in travel costs, and the driving force behind the creation of a Big 10 men's conference wouldn't be there, as I doubt that the Big 10 network is clamoring for more women's hockey as programming.
The biggest fallout of this is that there's essentially zero chance of Michigan and Michigan State adding programs until such time as the sport is large enough that BTN does want to show a lot more of it. The whole argument that it's Red Berenson's attitude that is preventing Michigan from adding women's hockey is misguided. I have no doubt that he's not in favor of it, but his support is probably not necessary for the school to add women's hockey, and it definitely isn't sufficient. The roadblock to its addition is the athletic department's decision to focus on other sports.
For much the same reason that a Big 10 conference is unlikely, the formation of one wouldn't lead to more east/west non-conference matchups, especially on the part of the teams left behind in the WCHA. Losing Minnesota, Ohio State, and Wisconsin to the Big 10 would do nothing to alleviate the travelling expenses associated with such games. I think a more likely result is some current WCHA teams either folding or becoming the shells of programs as the interest generated by being in a conference with the Gophers vanishes.
If Michigan and Michigan State were to add women's hockey in the immediate future, I think a better solution than Big 10 conference play would be for them to join the CHA, probably followed by a swap of Ohio State and Lindenwood in order to produce a bit more geographical balance. As I said, though, the chances of this are close enough to zero that we're just engaging in wishful thinking.