I am one of the core Nix developers, and hte one most involved with Dynamic Derivations. Yes, I'm aiming to massage the issue trick a bit on this, and write up a proper post going over what's left.

The short version is that dynamic derivations depends on content-addressing derivations, and content-addressing derivations has been in experimental-feature limbo for a while now. However (!), with a little push + judicious cutting scope, we can get the latter stabilized. And then the remaining road to stable dynamic derivations should be very smooth.

It's a more complicated story to tell because the work is a series of yak shaves, but it's not actually a huge amount of work.