Quick update, there is some working code floating around as a rough test case … 
(2x 4 split PSSM @ 1024, note the overlapping shadows and no double darkening on back faces). The best way to work this into the core is currently being discussed by some of the developers.
@nehon will be more than happy to explain how it all works, and is looking forward helping anyone who wants to implement it into their own project =)