Encryption certainly is a possibility for more and more agencies. Some doomsdayers on this and other internet scanning sites will tell you that publishing scanning information and talking about things we hear will ultimately encourage more and more encryption. Perhaps so, but I haven't seen any evidence of that. I belileve most public safety agencies welcome interest and participation from the public in their operations. Unfortunately you live somewhere where the elected officials don't feel that way.
I'd say more likely is the adoption of radio technologies that can't be monitored - Opensky, Provoice, MotoTBRO, Tetra, etc. These aren't encrypted systems, but ones whose manufacturers refuse to license the information that allows the creation and manufacture of radio monitors. Fortunately, in SC, the state has adopted an open-standard system (APCO 25) for Palmetto 800, and these unmonitorable systems don't have much of a foothold hear, yet. Fortunately, it's much easier for agencies to afford to join Palmetto 800 than to create their own closed system.
Other possible scenarios for reducing interesting monitoring opportunities are the increased use of private, commercial radio services (Nextel, Southern Linc, etc) and data systems (modern MDTs). But again, I think most public safety dispatch in SC will remain monitorable for the foreseeable future. Certainly within the expected useful life of a PSR-500, if you treat radios like I do.
Brian