It's easy to overlook that, by the end of the decade, there will be a surplus of EMU stock. That was true even before the delays to Transpennine and MML electrifications, factoring those in means we will likely see significant number of units going to storage and withdrawals. There will also be, for the first time, some real competition in the rolling stock market as the ROSCOs vie to obtain some revenue for their older fleets. In this situation, it isn't necessary for the operators to squeeze every bit of utilization from the older fleets, indeed it would probably be better commercially to have more slack in the fleet, and concentrate on a higher quality service with fewer short-formed and cancelled services.
We're so used to stock being in permanent short supply it's hard to picture the situation where there will be a choice of units available - although not necessarily in the ideal configurations.