If you watch Herman Li, he has discussed the PRS Breaking - and also said he was 'expected' to push it beyond it's limits' on tour to assess it and it's already been repaired by PRS.
Whether they do make a Herman Li Sig Model - even if just a Limited Run of 50 or 100 guitars - or not, I doubt that anyone will know about it until PRS or Herman Li announce something, We all know he has a 'Custom' built PRS guitar but doesn't mean he will become a PRS artist with a Signature model anytime soon.
Maybe they will, maybe they won't, but they certainly won't be releasing something until both sides are happy to do so. That could take 'years' of prototyping, tweaking and of course field testing on tours etc to see if they can be as 'reliable' as you expect from a PRS as well as work for Herman Li - feel right, sound right etc. Until they are both happy, they won't consider releasing a 'Signature' model, how long did we know about the MT100 amp?
Edit: Also Mark Tremonti had a Custom built PRS 'explorer-like' guitar that so far has never been released 'publicly'. He's had that a lot longer than Herman Li has had his unique PRS and he actually is a PRS Artist with Signature model(s)