What chance do you see of banning air-to-water heat pumps in WA or even MI?
Banning is out of the question. The whole thing needs to be regulated more precisely. The LAI guideline is headed in the right direction.
There is a law regarding the requirements for small combustion plants (1st BImSchV) that sets requirements and monitoring. For air-to-water heat pumps, there's nothing in that regard.
In my opinion, when applying for approval, the acoustic compatibility with the neighborhood must be demonstrated. This proof can easily be provided using the sound power levels from the data sheets. Before commissioning the system, an emission measurement must then be carried out (similar to small combustion plants), but not with respect to air pollutants, rather with respect to noise. Because my practical experience shows that, on the one hand, the sound power levels specified by the manufacturer often seem to be "far-fetched," and on the other hand, the installation situation of the devices is unusually often not at all in line with the state of the (noise reduction) technology.
Furthermore, the air-to-water heat pump units—also by analogy to the 1st BImSchV—must be monitored periodically, say every three years.
@TE: As has already been hinted here many times, you are legally, technically, and above all interpersonally on a losing streak with your installation situation. If the system location comes from the planner's pen: then I would have it redesigned. Cost-neutral, of course.