That's EXACTLY the solution.
Only, instead of getting "rid of" them, what we need to do is to have them become local divers in between their "dive trips to warm water destinations once or twice a year."
Convert them from "vacation divers" to "divers on vacation" and the industry will be just fine.
I know that shopping cart well. I was there a couple of months ago. If I stayed close enough to my buddy so that we were bumping into each other occasionaly, I could still see his light and knew where he was. Although it is much more expensive and only open part of the year to diving, there is a better option available to you, one where you can get over 30 feet of depth and swim endlessly around a wrecked Cessna in 5 feet of visibility if you actually wanted to see something other than gray silt during the dive. I believe that is the best you are going to do locally, though.I did my certification dives here in cold water, in a pond that getting to 22' means digging a hole. I saw the wonderful artificial reef (discarded grocery cart) and the life underwater was breathtaking (crawdads). I would not say the local diving is what drives my desire to continue my participation. It is in fact the 2 trips per year that are far more inspiring.
Colorado has among the most divers per capita of any state in the nation, but you are not going to turn any but the most rabid of them into local divers. When I look at a map of the U.S., I see a lot of states that are probably very similar. I have also seen the efforts local shops make to turn their clients into local dives. It doesn't work. If you say you want to eliminate the vacation diver, you are eliminating about 90% of the divers in the majority of states in the nation. Do you think the local dive shops in those states will be persuaded by that argument?
I myself experienced something very similar recently in my tech instruction. I was working within an agency that has divided tech courses into about twice as many steps (individual course certifications) as almost any other agency. Between each step is a requirement for experience dives. For example, in between the completion of one of their trimix certifications and the beginning of the next class, a diver has to complete 20 trimix decompression dives between 200-250 feet in depth. Any idea how long it will take a Colorado diver, with the local options described above, to pick up that many dives? (I know a tech instructor in Florida who told me he only does about 3 dives a year in that depth range.) You can only dive to those depths on trips requiring travel, motels, and restaurants. In the entire range of their trimix dive certifications, the agency requires 95 such experience dives in addition to the dives done during the classes. Any guesses how many years any diver living in the heart of the nation will need to complete those requirements? In essence, the agency made a decision that full trimix training will only be available to independently wealthy people living near deepwater sites.
I am sure I would have been a much better diver (in theory) when I finally reached that final certification level than I am now if I had stayed with that agency, but I opted to switch to one that would allow me to complete my training within my lifetime. That training was plenty good enough for the diving I do, and I have no regrets.
I think my situation is analogous to the many thousands of people who dive safely during occasional vacations. You can set up requirements that demand that they go far beyond what is required on those occasional vacations, but don't be surprised if they go a different route.