A rescue conundrum

Here's the problem. There's this dog. He's a young, black, male German Shepherd. His owners want to surrender him. Young married couple, three kids, no time for the dog, that old story. The dog is house trained, crate trained, neutered, vaccinated, and socialized with three kids.

Normally I'd jump at it, sounds like a easy to adopt dog that would be sought after by many people. But the dog is disabled. He came from a backyard breeder, a bad decision that turned out to have consequences. He's got a wobbly, floppy rear end. He can't run, can't jump, or do stairs.

I'm not sure of the cause or if there's a fix, so I have to assume that there isn't for the purpose of making an intake decision. Given this, I'm not sure the dog has any prospect of adoption. If I take him in and can't adopt him out, he takes up a foster spot in someone's home indefinitely, and that home is most likely mine. So then I'm stuck with the choice of keeping him for the next 12 years of his life, passing up other, adoptable dogs for lack of space, or putting him down.

If I don't take him in, the owner may or may not live up to his obligation to the dog. That's the kind of conundrum we deal with in rescue all the time. I'm trying to get the dog examined by my vet before making a decision. That's the best I can do.