Why is Swain getting a rework?

Because "Press R then run around in circles and Zhonyas when you're low" isn't exactly interactive gameplay

Cause he needs it badly? He's unfun to play against, is very binary (when playing) and has really old visuals

Its because his kit has become boring and non-interactive. You press R then Hourglass, that's pretty much his combo.

He's as fun to play as Mundo vs several Grievous Wounds characters, which is brain-dead boring.

He needs to compete with Ryze