It's possible, yes. But IMHO, they're just going to look like... shaggy mutts.
There are 1000's of dogs like this in shelters all over the place.
The Canis Panther is a combination of Doberman, Great Dane, Black Lab, and American Pit Bull Terrier. Although I'm not sure the proportions. This is not a recognized breed, but I do find them attractive.
But these breeds are somewhat similar type - all have drop ears, 3 of the 4 have VERY short hair and Labs have quite short hair. When you start mixing this and that (example - a GSD has prick ears and sometimes LONG hair) you really take away from all the other nice things in the other breeds... just my opinion.
I don't have anything against mix breed dogs, but I would hope that if someone is setting out to produce them, they would have some VERY solid reasoning for producing more puppies, that are essentially, mutts.