I mentioned possible modifications of the existing design - different, but not too much different.
The shuttle derived vehicle proposals of 20 or so years ago (and occasionally revisited for some years thereafter) would have made some sense. That could really have saved money by economy of (a little more) scale, shared components, spare parts, etc. As it was, the reusability was mostly a mirage, and cost per pound to orbit reductions were entirely a mirage. So maybe the SDVs would have worsened the problem, and wound up building in even more inertia.
The main reason for the new booster not being SRB-based (and therefore shuttle-derived) is that they A) puke out some pollutants and I think the new booster is all-cryo (water being the exhaust); and B) that the SRBs are expensive to recycle. The new booster will be cheaper and expendible, and pretty hot to trot. :')
It's amusing that expendible boosters turn out to be cheaper, considering the mantra of recycling that has prevailed for over twenty-five years...