Could be true. I read that Yamaha was bringing out a YZ500 for 2020 in limited quantities. It was something like 70HP at the rear wheel.
I last raced the 250 C-class in 2000-2001. I was young then, but 250cc 2 strokes of that era were violent when they hit the power band. I'd be terrified of what a modern 500 would do; maybe they're more mellow now?
Link:
http://dirtbikelover.com/2020-yamaha-announces-limited-yz500/
Edit: That link could be a hoax, considering there aren't many corroborating links. Who knows? I think there's still a company that makes CR500AFs if you really want one...I know they used to back when I was into it. I'd be scared to take one around a track.
Edit2: Two strokes in general are making a slight comeback. There's a large segment of riders that are nostalgic towards them, as the 80s-2000s were kind of the MX 'hayday'. Secondly, they're way easier maintenance wise. Yamaha has 125/250cc 2 strokes back in the mix, and as you said, KTM never stopped.