With the pronounced ridge that a baseball bat handle has, I can see how that would be considered a nonconforming "bulge" per rule 3, but if it didn't have that ridge, I don't see how it would be nonconforming if the butt end were 1.75" or less in diameter and simply tapers from there.
I myself would like to try something similar. Something like a jumbomax size end cap that then quickly tapers down to a midsize, reduced taper profile for the rest of the grip