I believe Chill might be encumbered by patents so I'm not sure an open source
implementation is legally possible.

https://patents.google.com/patent/US20080055318A1/

It's also quite a bit more complicated than a static framerate limiter,
requiring monitoring of on-screen movement and input events to constantly
evaluate what framerate is appropriate in each moment.

A static framerate limiter would be nice though, but we already have
libstrangle for that which works well most of the time.