People who claim that classic+ will cost too much money are not right. One user here claimed it could cost hundreds of WOW TBC Gold millions. Do you smoke? They already have a very solid platform for classic. There is already a lot of content by just being pure WoW. In addition, adding a new zone class changes, world boss, etc will not cost thousands of dollars. The original Blizzard game was a huge commercial success. Take a look at the massive server problems at launch and the Twitch statistics. Seasons of mastery won't attract an increase in players to WoW. However, I believe classic+ could. Today, RuneScape's old school is still being used by new players. That's also an old game however, since they've updated it, people aren't feeling like they're being a waste of time.
It's not that big a number for classical+. A simple tier set for off meta specs is enough. Adding new items off bosses isn't a lot of work. The prospect of a new raid is more expensive, however one buy Burning Crusade Classic Gold that I would like to be a part of. While I'll always question the possibility of a new scenario, I am optimistic about the future.