Well, I know someone else is making a more full-bodied total conversion of this, but if you're just after a gameplay mod that can plug-and-play with existing WADs, this will do the trick.
Contents:
sphot.pk3 • More accurate "SUPERHOT" emulation in Doom using custom monster and weapon definitions
sphot-u.pk3 • Universal "SUPERHOT" script that adds time-freezing rules to most games and mods
The Universal .pk3 is fun to play around with in various games; I have played through a great deal of Hexen with it and I imagine it works well with anything that does not use heavily scripted effects. Mods that use scripts to perform status changes over time on players or monsters will break if you use this, as the scripts do not respect time freezing powerups.