On the AOL message board, one woman had a large breed of female and a small breed of male. Both purebred, though I forget what breeds, and neither one fixed. The female went into heat, and this woman didn’t bother to keep the dogs separate, as she figured that the male would never be able to do anything without the aid of of a trapeze, or at least a stepladder.
A couple of months later, she had a litter of puppies. She said that the hussy laid down for him.
In the cross-breeding genre, it’s second only to “Can humans mate with chimpanzees?”
HA! I have that issue! As I recall, there were two offspring: one as you describe, and the other with a giant head on a chihuahua body. The big-headed one told his story to Fat Freddy’s cat, calling himself a “Great Wawa”. He introduced himself, then said, “I know what you’re thinking…he stood on a chair.”
Chihuaha’s have been responsible for a lot of mongrels. Males can mate with larger dogs much to the owners surprise. Great Danes?? Nah, but they can dream. 
Oh dear, now I *really *want an 80 lb dachshund.
About 20 years ago I saw a German Shepherd / Dachshund mix. Freakiest thing I ever saw. A Dachshund body with a German Shepherd head and fur. Looked like something a mad scientist would come with. Wouldn’t have believed it if I hadn’t seen it.
Takes me back to the first The Straight Dope: A Compendium of Human Knowledge book by Cecil Adams.
Q: I think my roommate is having sex with his cat. Is this possible?
A: No. You can’t park a Cadillac in a closet.
Made me cry I laughed so hard. And thus another Doper was born. 
Only after I get my bread-loaf-sized bear.
Contrary to common opinion, a dog’s genital size does not match it’s overall size. A Great Dane in fact has one of the smallest. Next time you’re around a dog park, take a look at the impressive schlong a cute little Bassett Hound is swinging under the length almost of his entire body.
Bassett Hounds are not little; they weigh up to 70 lbs.
If the parents are purebreeds, then the first-generation hybrids should all be pretty consistent (though I don’t know what size they’d be, and they might be oddly-proportioned). Breed two of those first-generation Great Wawas together, though, and there’s no telling what you might get.
First, more on big dog small dog hybrids - Miniature Goldendoodles - including toy poodle/Golden mixes.
From a table attached to my previous cite it seems like the first generation is, if anything, more all over the place than subsequent ones, albeit there may be a selection bias in the breeding of next generations for nonshedding.
I do understand the logic of your argument, yet the more mixing that occurs the more dogs seem to move to an archetypal generic dog type.
I saw a pit bull’s head on a dachshund’s body once, a one generation mutt. My feelings were exactly the same.
Movie correlates: The Fly (the first one); Clockwork Orange
They did catch him hanging around the elephant enclosure at the zoo next.
Not quite as extreme, but my mom’s mutt we think is a beagle-German Shepherd cross. Which actually turns out to be a very good-looking cross.
I once saw a Shepherd/Corgi mix. Looked pretty much the same way.
I think I saw a dog that was half Chiuaua and half Dane. It looked very weird. I mean, I cannot know 100% if the owner was telling the truth. But it definitely wasn’t the best combination out there. I thinkt hat there are more beautiful combinations than that one.
One of the weirdest mixes - and ugliest - I’ve seen was a chihuahua/pug mix. It had a perfect pug body and a perfect chi head. Looked like some kinda mad scientist experiment, and was bad tempered to boot. Just wrong.
This article may be of interest to some.