That, especially the barbarian progression, would have a lot of other impacts rippling through (qualification for feats and prestige classes, increasing the power curve especially when they already get a bonus from rage, etc.).
I don't know the original intention, but from my understanding tieing BAB to HD was a side result, not the intended goal. I think the intended goal was to give wizards and such more hit points. They are quite frail with the kind of damage 3.x throws around. Tying HD to BAB is more like a nice shorthand for knowing how to convert any other class out there, and is an after effect, not the actual goal.
Put another way, I think the problem being solved here is "too ow hit points", not "HD and BAB should somehow be related".
Oh, I should've added in there, that if you want to keep d4 for wizards and such, that's cool. I think this is a case where Jason is trying to fix a problem you don't have which is likely to happen to most everyone when someone is trying to fix the rules.
My main point was just that if you want to keep d4 for wizards, then I wouldn't bother with the BAB/HD relation since that's not the problem he was trying to fix. That's all. :)