Yeah having a per-instance time scale is in the backlog somewhere, and doing this is currently a pain, as you have to manually scale every time-dependent value processed by any evolvers (scaling velocity by the time dilation factor, switching a constant accel in a physics evolver to a per-particle accel scaled by the time dilation factor squared, etc..)
This is something that'll most definitely be in pkfx v2, but we currently have no specific plans for it in v1.
v1.12 is currently in the pipes (spoilers: with attribute samplers at evolve :) ), maybe we can consider adding the feature there.
We'll take a look at how much time it would take us to implement this, and if we have the resources to, we'll do it.
If you want to discuss it more drop us a mail on support. (And if anyone needing this feature reads this, please send us a mail as well, or comment here)