If you have a PC, you can receive and decode NXDN, MotoTRBO, P25 and X2-TDMA for about $25 using DSD and an RTLSDR
^^ This.
You wanted to know what the next generation of scanners will be? That's it. SDR. From there, the sky's the limit. With an RTL-SDR and the right software, you can theoretically decode or monitor just about anything.
P25? Yup. X2-TDMA? Yup. NXDN? Trbo? Provoice? You bet. Even encryption?
Sure, it's possible, and been done. RD/LAP (Mobile data terminals)?
Yes, that's been done too. What about mobile video/COFDM? Why not? It's just a matter of writing or obtaining the right software because your "scanner" is a dongle connected to a computer.
Yeah, sure but what about portability, you say? Who wants to lug around a big desktop or laptop computer you say?
Fear not good citizen, there's a solution for that too.
I think the scanner of the future will be a portable computer like the Raspberry Pi, mated to an RTL based SDR which will come as a "blank slate" for folks to load up with GNU Radio, DSD, OP25 or any other variety of free SDR software available if they wish. For additional money, paid software packages could be made available to download from the manufacturers that will work across a common set of hardware, meaning that you could purchase your scanner hardware from GRE or Radio Shack, download a P25 monitoring suite from Uniden and then add on a spectrum analyzer from AOR or a video decoder from iCOM or dozens of other possibilities. Maybe ACARS is your thing and the WinRadio people release something cool for ACARS monitoring that you'd like to try. Again, the sky's the limit and if everyone builds to the same basic SDR hardware, costs will come down. I think that'd be a win-win for everyone.
I could be wrong of course, but this is where I see the industry going and it would be a boon for hobbyists if it did.
-AZ