There is no reason why a patrol officer in say Suffolk County NY needs day to day ability to talk to a patrol officer in Buffalo, six hours away.
This is an example of why most interoperability solutions don't work or don't even get used.
If you're not using any solution on a regular basis, it isn't likely that it will be used under stressful emergency conditions either.
Incident commanders are reluctant to switch and use something that all involved don't train on and use on a daily or at least weekly basis. There is far too much risk in "losing" people/crews if/when under these situations, they end up on the wrong channel/talkgroup/zone, etc. Incident commanders are primarily responsible for responder safety and accountability first. When unusual radio procedures are used and some ends up in the wrong place, the IC has no way to know some aren't getting the message that might save their life.
For these types of situations, I firmly believe - like on many other situations - that the communications/dispatch centers should play a key/primary role in "making things happen" for the people they are supporting on the street. These days, I hear more and more dispatch centers providing additional verbal information to responders over the radio to eliminate the need for those in the field from having to read data terminals, look at map books for hydrants and hose lay distances, etc.
For many years, dispatch centers have established patches between users and systems. If there is a need for a 'group' of users at one location on one system to be able to communicate with another 'group' of users working the same incident, doesn't make more sense to have that communication enabled in a single location verses requiring dozens of first responders in the field having to stop what they are doing (maybe they can't) and fiddle with their radios - changing zones, finding the right talkgroup, etc.
During a recent incident on a major highway in northern Maryland, the dispatch centers in two non-adjacent counties were able to cross patch talkgroups from the native systems together such that the units responding and operating out of their normal area were able to continue using their normal system/talkgroups.
Adding more systems/functionality and complexity that is/are rarely used isn't going to help anyone but the system vendors (line their pockets).
Perhaps technologies to significantly improve the communications/dispatch centers ability to rapidly provide good quality patches between systems. This seems like a simpler and more consistent way to provide interoperability than placing all of this on an already stressed first responder that is trying not to be injured or killed during an emergency.
Other options to consider include roaming and ISSI capabilities.
We can move around and use our smart phones without having to switch anything .... and most of these public safety systems use newer and much more expensive technology. What is wrong with this picture?