Tawnos
A guy with a bass
Historically, ~10 years between expansion rounds tends to be the safe bet. It's really hard to imagine that happening as things stand right now, but I suppose that's why they leave big gaps in between rounds.
A lot depends on cities booming and seeing themselves as big-time (think Columbus, Raleigh, Vegas) because that's really where the expansion opportunities are. It's where you get communities eagerly throwing money at arenas to attract a team, treating an expansion team as a big deal rather than just another option in a mature landscape.
I'd keep an eye on the south and west, where the population is growing rapidly. Texas (Houston, Austin, San Antonio) and California (San Diego, Sacramento) have large cities which are under-served with pro sports. Portland is also in that category. Fast-forward those cities by a decade and get lucky with an owner/arena situation, you've got a docket of potential NHL cities in those two states alone.
Houston is a bit of a holy grail (along with another stab at Atlanta? We are talking 10 years from now).
Austin fits the Columbus/Raleigh mold extremely well and their growth is explosive. By 2030, there might be 3 million people there.
Thing about San Antonio and Sacramento is that, while under-served overall, they both have NBA teams in place. Ditto Portland. I wonder how much of a barrier that is.