Many RepRap controller firmwares support Firmware Retraction via G10/G11. (See http://reprap.org/wiki/G-code#G10:_Retract
I know this has been asked for in the past so I was hoping to see this added to version 4 but it looks like I'll have to continue to wait. I just took a glance at the exiting feature requests, and I'm surprised to see it doesn't seem to have been asked for recently, so I figure putting my two cents in might help.
Having the ability to allow the controller to handle retractions instead of the slicer enables users to adjust retraction settings on the fly which is immensely useful. Some examples include: tweaking retractions when switching from one brand of filament to another, or for when dialing in retractions when working with a completely new filament or printer.
Firmware reaction is supported by a number of other slicers, and I imagine this to be very easy feature to implement since all it requires is for the slicer to simply issue G10 and G11 instead of it's own retraction moments.
Adding something simple like firmware retraction would help bring this wonderful slicer up to feature parity with some of the open source alternatives.
(NOTE: I'm aware there is a way to accomplish this via post processing script, but what I'm looking for is a simple checkbox to enable it without messing around with post processing.)