You could associate it to a bang with something like mzScript...or an alias to LSXCommand...or just use an evar in the step. Your call really.

Shortcuts were removed from themes basically to allow for portability. The shortcuts on your machine that you want and use differ from those I want on my machine. We did find repeating application types and were able to come up with the basic evar setup when OTS1 rolled out, but there really isn't anything else to be added. If you want to add shortcuts to your theme you can of course...just requires a little more work on your part.