I'm not so sure it lowers their power numbers as much as you may think, with the assumption that an arena is planned for a few seasons out. This is what, their second year of existence? They've already brought home a trophy from Vegas, beating an upstart NMU that's come out of nowhere this season, and while the Huskies have been pretty good, I think most would say it's been a slightly disappointing year considering the last few seasons. But Tech did beat a ranked Boston College, so I think they are a better team than their record seems.
Now imagine ASU have a real arena and proper facilities (I'm honestly not aware of what they have now), and able to attract even bigger name recruits. I think the NCHC would take the initial risk for the future profit.
Now what does the WCHA do? I think you have to make another pass at them, why wouldn't you? I don't think most people would mind having another power school like ASU in the conference, the big problem is the travel. Again, I don't know the details of what was offered before, nor do I think anyone does, but unless they jacked up the travel subsidies they would have to cough up, I'm not sure what the league can really do to sweet talk them into joining the WCHA over the NCHC besides something like guaranteeing a playoff birth for the first X years.