As far as I know, a good majority of this new system is already in place. I think the license has even been granted already.
Towers exist in the locations shown on the license (at least some of them). Now I'm not sure if the actual radios for the new system are in place as well as the antennas needed but that can be swapped fairly quick. Swapping out mobiles would take a long time.
The agencies that join will be fine but if anyone keeps the old vhf point to point channels active, then that equipment will need to become compliant.
Most halfway recent equipment will be compliant already with a change in the radios programming. And of course a license modification showing the bandwidth change but that is free of cost.
Still not a super big deal figuring those channels are generally not used in a mobile environment.
My guess is that most smaller municipalities will be slow to move to this system if they even move at all. It will be on them to become narrowband compliant for those using VHF frequencies which is a good majority of the users in the county. There are a lot of UHF (450) users here also but I think a fair majority of them are already using 12.5 kHz bandwidth.
It will be interesting to see how this plays out. Maybe nobody will join and the system will end up being used by just the official county agencies and departments. I'd guess that several have promised to join though.
Are there any incentives for a small municipality to join into this new system?
I would think many will end up with much worse coverage than they currently have now. Then some will have better.
Some of those sites (the ones that don't exist) were pro forma locations to establish perimeter contours. The prevailing theory was that you can build an aggregated contour with your worst-case locations, then when a vendor comes in to specify where they want the system, the license would be modified so that the contours from that location are contained within the aggregate. Make sense? Step 1 locks in some resources no one currently has. Those resources could then be moved around on the basis of the selected vendor. Step 2 then finalizes the location.
I don't think "swapping" fixed-end assets would be an accurate term. The legacy system would have to remain intact up until optimization, cut-over, more optimization, and acceptance, so the towers would need to support the existing VHF systems, as well as lower-loss cable and focused directivity 800 MHz antennas (you want all that power beamed into the streets where you need it, not going out to Calloway County). That would also mean 2 radios, unless they buy $7 grand two-band mobiles. The sales point for that is that those mobiles could roam onto MOSWIN and go anywhere between the pockets of 800 and VHF land.
Only the most very recently licensed systems (after Jan. 1, 2011) should be considered "narrowband compliant." A handful were before then, but it's only a handful. You're right, for most things it IS a matter of programming, but programming = labor costs, whether it's done internally by a competent person, or whether it's subbed out to a vendor. Reprogramming will also potentially disrupt any simulcast configurations, which are highly critical to frequency and phasing. So it's not so simple for the more advanced systems (even if they're simplex).
Regardless of whether it's kept or migrated to a talkgroup, things like "point to point," "sheriff's net," "'federal' mutual aid," and "fire mutual aid" still have to be narrowbanded to fully work with everyone else who's not requesting a waiver.