I agree that the rolling stock for the next franchise is still extremely doubtful. There is an opinion though that any Class 150 stock once PRM▸ modified will find work for many years, so I'm not sure that only doing half would fit with the lessor's intentions. Besides, there is no indication yet that any derogations will be permissible. Whilst I suspect some might be allowed for a few months whilst new stock is delivered, I don't think a two or three year period of grace for rolling stock that is likely to be reused beyond that date will be.
The issue is that, outside the ValleyLines, the Wales & Borders franchise has VERY, VERY FEW short-distance services where class 150s are suitable. Unless there are service frequencies improvements on certain routes or a new, non-electrified, metro network in the Swansea area the number of 150s required could be counted on the fingers of one hand. Class 150s are uncomfotable inner-suburban stock which should not be permitted (except in an emergency if the booked unit fails) on any service which ommits calls at any station on its route or with a journey time exceeding one hour.
So I think all the Class 150/158 will be modified by the deadline. The elephant in the room is what is going to replace the Pacer stock, and how will it be ready in time? The betting now has to be on further 319 Flex's being ordered, as they or the D train appear the only viable options within the timescales once the franchise is let, and the Welsh Government has nailed its colours to the 319. My only doubt in this argument is the CAF assembly plant recently announced, where there will be a strong political benefit to placing an order with it. Though that would mean an extension on Pacer lifespans beyond 1/1/20.
The Flex units are the best option I can see for Pacer replacement in Wales in my opinion, particularly if they can be given an outer-suburban interior suitable for journeys over an hour from Cardiff/Swansea to Cheltenham and Hereford. Where CAF might come in is the new
EMUs▸ to replace the 150s on the ValleyLines and/or trams for Cardiff Bay (I hope not the ValleyLines proper to Merthyr etc. where journey times dictate that the very limited seating (lots of standing room) of a tram is inappropriate). There will also be a need to bolster the long-distance fleet, and CAF's mark 5 coaches are currently the only long-distance stock on the shelf other than 125/140mph intercity units. Perhaps they could also modify their class 397 design slightly (with end-doors on all coaches) to make an alternative to mark 5s, but sadly their units so far don't have unit-end gangways (
UEGs▸ ) which I think should be a requirement on all new units for Wales & Borders. Only Hitachi's 385s offer UEGs at the moment and they are only really an option for the ValleyLines (once electrified), unless Hitachi can do a diesel version with an intercity door layout.
My other big worry, along with swarms of ex-Valleys 150s cascading onto long runs like Pembrokeshire to Swansea, is the mark 3 sets. There is not going to be any PRM-compliant stock available with an intercity door layout before the mark 4s come off-lease in 2020, since new units take too long to build. The only options are a downgrade in quality (using flex units or similar), an expensive rebuild of stored mark 3s to PRM standards to replace the current mark 3s (leaving the next
TOC▸ with a micro-fleet of mark 3s) or a derrogation until new stock or mark 4s are available unless CAF can squeese in a batch of mark 5s in time for the 2020 deadline.