I don't really have an answer to that, it is an interesting question. For me personally I don't hold any attachment or feelings to the bodies of the deceased. When I die I'm getting one of those mushroom suits that decomposes you and quickly returns you to nature. But some people are much more attached to the bodies of the deceased whether for spiritual reasons or otherwise and I can't really speak for them. Would eating the euthanized pets cause suffering to their previous owners, I really have no answer for that, I assume there would be some people who would suffer from that and some who wouldn't mind. The quality of the meat I think would be very low though considering it would mostly be very senior animals with many health issues.

If the only animal corpses anyone ate was euthanized pet remains and the practice was somehow free of influencing the unnecessary euthanization of more pets, I can't say I care. Same way I don't really care if people eat roadkill or animal products from a dumpster. I'm not going to do it, I don't see these things as food. And I think there's a minuscule harm done in the proliferation of the perception of these things as food. But that harm is negligible in the face of animal agriculture which is my primary concern.