As if anyone will pay for the privilege of developing apps on a platform that makes breaking changes on a whim.

Discussion about primary source: https://news.ycombinator.com/item?id=34622788

Won't this just have the effect of rendering Twitter's data/product less relevant?

Sure, they should be paying us to post there

Amen, brother! Twitter users' Valuable Intellectual Property is the sole and only thing that supports Twitter, and people have just given their IP away.

Will this affect SSO with twitter?

Mobile SSO has already been broken on Twitter for a few months. I’d begrudgingly pay for SSO for my app.