Granted some stock, especially fixed formation >4 cars is route captive but much isn't. I also get most surplus/stored stock is EMU's but how many routes are we running diesels under the wires for point to point journey convenience vs re configuring services to maximise point to point capacity with stock that's available. This needs an industry wide task force to determine whats required where and with railways effectively in government control they can disregard the commercial matters that get in the way of taking the right decisions in a timely manner to enable the network to move people from A-B where there is demand need and current capacity shortfalls.
The trouble is that even if you could remove all the technical obstacles to redeploying stock, there remains the issue that staff training would likely be required, and there’s already a backlog of training across the industry.
I’d say any tweaks are likely to be just that - shuffling things around within the boundaries of what’s already do-able, rather than pushing those boundaries outwards.
It perhaps doesn’t help that at present we don’t really know how things are likely to pan out. Peak services with high capacity are still fairly quiet in places, whilst we have early-morning services going over limits. An operator could shuffle this round, only to find there’s a shift back to traditional times if people start returning to office work.
It might have been helpful if some more Pacers were available, however would there have been the depot capacity to stable and maintain them?