There are people for whom even $100/mo/user would not be a big deal but then there are bootstrapped businesses in 3rd world countries with lots of non tech part time employees (I want all of them on same communication medium). For them its not an easy decision.

This is not to claim Slack is pricing it utterly wrong. Of course they have their target audience and should do things best for their business.

Agreed. And for startup teams where $50 a month for 5 friends is a lot, it's 'limited' free version isn't very limited at all.