The fact that they've ramped that stuff up so much in the last couple years does not bode well for the future, in my opinion.
My installation isn't associated with a business, it's just a chat board for about 30 people, so there's no question of me being willing to pay $300 a month for the privilege.
I'm sticking with Mattermost because there's no better option, and I've got hundreds of thousands of messages I don't want to lose. However, it isn't like they don't try to extort you just because they're better than Slack about it.