Really it also comes down to....
Is it worth the investment?
Why go out and take the time for R&D, licensing etc for a handful of systems? ProVoice may take off or may be short lived as VSLEP was.
Other than the system may cost less than the other mainstream products, the goal lately is for users to be able to talk to each other with little or no 3rd party intervention. This is the problem that system managers are facing...
If I have brand x radio, what will I have to do so that my users can talk to brand y? What will it cost? Is it worth it? Should I spend a little more/less on brand y?
EDACS itself most likely isn't going away anytime soon like all the Type II systems out there. However where grant money and state/federal mandates come into play, the only choice may be a APCO25 complaint system...which is neither EDACS, Type II or OpenSky - But an APCO25 conventional system or 9600 Trunked system.
So, with that said....the IMBE codec that was selected is an OPEN standard so that anyone willing to pay the licensing fee can have it. VSLEP is propriatary to Motorola. ProVoice is a IMBE based codec developed for MA/COM as is OpenSky's AMBE. Depending on how popular the "other than APCO" systems sell, and where they are located will dictate a scanner based on them.
As for the comment about going out and buying a radio and programming it up, those days are slowly coming to an end as well. OpenSky has some pretty specific security features that will not allow a radio to Rx even if programmed properly...it needs to be activated via the central controller or via a software key. Motorola also introduced a similar system. My new XTL5000's are defined by Serial number, Model number, flashcode AND ESN (like cell phones). They have also introduced limited system keys for trunked systems as well. No more basement flashing (for now at least!)