I'm personally against the introduction of "B scale" terms and conditions for new joiners, it's a classic industrial relations strategy to divide the workforce. I know that in the case of Protected Staff from the BR days such a system exists, however they spent many years on very low pay which newer joiners like myself didn't have to go through. ASLEF need to ensure that if the railway is to be run as a privatised system with competition between TOCs, then such competition applies to the retention of staff. A universal B scale means that employers don't have to work anywhere near as hard to retain those who are on the A scale.
If the DfT don't like the idea of competition pushing up salaries, then they should offer a universal contract with everyone on the same conditions with location (cost of living) and possibly work difficulty allowances. I think it would be reasonable to suggest that 12-car DOO should attract a higher "difficulty" payment than a two car with a guard, other things remaining equal. Obviously, the cost of everyone being on the same deal is that it'd be easier to argue they work for the same employer, hence making one dispute potentially applicable to all locations.
I don't necessarily think it'll be easy for the DfT to reduce traincrew T&Cs across the board, they'd have to decide whether to do it one TOC at a time, or a uniform imposition across the entire network. I don't think the latter has been tried since the Flexible Working Dispute in 1982.