Looking at the timetable changes in May, it looks like the current weekday journey between Holyhead-Llanelli and Llanelli to Chester is no longer worked as a through train from Holyhead to Llanelli, it starts at Cardiff Central and still goes to Llanelli. So there will be 2 diagrams for Swanline (much like before Covid but without interworking with HOWL) and with them both ending in Chester in the evening it would make sense if they were either 197s or 175s (or diagram of each perhaps) otherwise there isnt much point in ending 153s or 150s in Chester given most routes up there should be 197s by then, aside from the 158s that interwork with the Cambrian.
Im really hoping for 197s (or at least 1 197 diagram) if enough train crew at Cardiff can be trained in time. If not will just be happy to see a proper Swanline stopper returning.
What im thinking could happen is if some Holyhead to Cardiff are switched to 197s in May, some will end in Cardiff at night and do Swanline before returning to Chester at the end of the next day. This is just me speculating, no inside knowledge.