Pure speculation on my part but I'd expect to see the 0955/1445 Nottingham-Skegness and 1215/1724 return to be one of the GC HST sets next summer, releasing 2 x 2 car 156/8 for use elsewhere/PRM mods...
Can anyone confirm whether EMT's 156s are going to get the PRM mods???
Very unlikely to happen as it involves fiddling around with the long term planning diagrams too much, there are only 13 Senior Conductors who sign HSTs, and a similar number of Drivers. To put it on a daily diagram requiring two running turns would stretch resources a lot. I can't check right now but I'm also pretty sure that some Boston drivers work part of those services too, so that would either require double manning or movement of work between depots (which is easier said than done).
We also end up with issues where the HSTs would be calling at Radcliffe, Bingham, Bottesford, Heckington, Swineshead, Hubberts Bridge and Wainfleet, stations which are far too short to reasonable accommodate them and haven't seen a scheduled slam door service for nigh on 20 years now. The risk of a passenger unfamiliar with the trains alighting from a door not at the platform is probably too great.
They're an absolute pleasure to work on the Summer Saturday extras but the diagrams there are usually restricted to working the HST only, and I'd love to get more regular work with them, but its not going to happen.