Because today was another day where I went nuts trying to figure out retiming to be 'right', I now took a bit of time to build this retimer, which works a bit more intuitively.
It works via a solver - so now you can animate the speed of the input, like in Premiere, and the output duration essentially gets stretched and squashed automatically. Because the solver is simply a recursive calculation, the solving is instant - when you re-animate the input time, just hit "Reset Simulation" and you're good.
Maybe it's useful to somebody! Here it is for download: retime_solver.hdanc (H17.5)
(While it's just a non-commercial asset, it can easily be rebuilt in a couple of minutes. The groundwork is done.
All the best,
Martin
PS: I also added a fun-toggle, where you can tweak your retime with spinning test-geo in case you have heavy input geo! (... which we always do, right?)