So one of the things people aren't noticing about Seattle getting a team is where it is located in the United States. The NHL doesn't have a team in the Northwestern USA. They have the Canucks in that area, but that is obviously in Canada.
So why is this important? The NBC deal is coming up after the 2021 season, which also happens to be when Seattle is planning on entering the league (pending a possible lockout of course).
Having a team in all four corners of the USA is imperative for the NHL if they want a better TV deal in the United States. Right now they are near the end of a 10-year, $2 billion deal with NBC after regrowing the brand after the 2005 lockout. The hope on the NHL side is to create a bidding war with ESPN for the coverage and gain some more media money.
In the early days when the NHL first tried to get a national TV deal it was the original 6 days where it was mostly in the Northeastern USA. The networks laughed in the owners faces because it was essentially a regional sport. That's why the league doubled in it's first expansion in 1967 so it can say it was coast-to-coast.
In a similar context, it is also the reason why it fought so hard to keep Arizona where they are. Had the Coyotes moved to Hamilton in 2008-2010, they wouldn't have had a market in the Southwestern part of the USA, which would have hurt their deal with NBC in 2011. Now, however, Vegas being a much stronger market in that area, I'm not sure the NHL would oppose the Coyotes moving. (See Houston)
As far as Quebec goes, they will never expand there. The purpose of expanding is to create new fans in new markets. Quebec is not a new market nor are they new fans. The fact is, whether or not a team comes back to Quebec City, the population there is already consuming the NHL. There is no pressure for them to move there because of that.
However, just as it was with Winnipeg, should a team in trouble need to move (specifically in the East), they will be the first choice. In the West, Houston will be the first choice if there is relocation just due to the logistics in the schedule re-alignment. Also it was one of the biggest markets in the States that doesn't have a team, and has a history with hockey in the Houston Aeros. The only reason it isn't already there is because Les Alexander (former owner of the Rockets), was upset when he failed to buy the Edmonton Oilers and move them to Houston. He put a clause in his lease with the arena saying if an NHL team moves in that isn't owned by him, the Rockets lease becomes null and void.
So yeah, a little bit of a history lesson, but the point is it all comes down to money and timing.