John,
That's correct. They had one computer that would be VPNed into. That one computer had many different plug-ins as most of the systems out there were the cheaper Lorex, Swann types. Other than the points you mentioned as the problems with what Albuquerque is trying to do, the biggest problem that all these agencies have the management of plug-ins.
Police Departments ultimately go to the model you mentioned, such as Detroit. Use one vendor across the board. I've seen agencies do this model but give that up because of pushback from businesses about the costs, coordination of installations and managing of even more hardware.
Installing devices causes more headaches than the Police Departments are will to deal with.
I just saw a Night Owl 4 channel for $250. It's hard to convince a small business to pay a lot of money for to make a system compatible with the PDs VMS. Detroit has been telling the businesses that they will monitor their store front 24x7 from their RTCC, even though their MOU states different.
I haven't seen other agencies do this because it's potentially major liability for them.