In theory - yes.
In practice - I'm not completely sure how it would work.
Most of these people who want XL Bullies seem to be young, fit men who want something that makes them look extra macho. If anyone is physically capable of restraining such a dog, it's probably the majority of the people already buying them.
Of course, I'm not convinced many fit young men can restrain an XL Bully who is hell-bent on attacking....
... but how do we account for the differences between two dogs of similar weight - like an XL bully and a Newfoundland? One is much more muscly than the other, and much more likely to do damage. The worst a Newfoundland is likely to do is to drag you out of the water because it can't tell the difference between your inelegant front crawl and drowning.
How would we test for the ability to restrain such a dog? What parameters would be set, and what margin for error would we allow? How would we allow for the natural changes in strength that someone has over the next 10-15 years?
If, in ten years time, the pup has grown into something mild-mannered but the owner loses a leg in a car accident, do we take the dog off them? It would seem an overreaction.
Most - but not all - of the fatalities have been people attacked by their own dog. Fending off a dog that's attacking you is harder than simply restraining one that's trying to lunge at someone else.
There's also a risk that we create a scenario where a few people are stopped from buying XL Bullies, but "I passed the test of strength to have an XL Bully" becomes an extra macho status symbol, and makes them more desirable.