I just stumbled across this article shared int the TrainerRoad forum about response rate to CTL increase.
https://alancouzens.com/blog/athlete_type.html
It is accompanied by a calculator which determines response rate based on two past CTL and FTP samples and given a third (future) CTL gives a predicted FTP
https://alancouzens.com/blog/training_responder.html
Seeing as the equation for response rate seems to just be the slope between two points on the FTP/CTL plot and intervals.icu has plenty of data it seems like a response rate metric and FTP prediction could be quite doable.