Porterbrook have decided reforming the 153s in to 155s would cost too much. Given how much work has been needed to keep an existing 155 in service, I imagine they were right when they said that!
Arriva drew up a fleet plan for Northern which makes both the Pacers and 153s surplus to requirements by the end of 2019. There should also be some more 170s (or equivalents) joining in 2022 for extra capacity.
If the entire Class 153 fleet was converted back to Class 155 units, it would produce 35 two car units (155301-335). It isn't beyond the realms of possibility, but I just think it's very unlikely to happen, particularly if Porterbrook's Class 769 bi-mode is a success.
This 155 refurbishment clearly went way overtime... but it was the first one, so the subsequent units will at least be a known quantity. In theory by the time they've done 6, the final one will be a doddle

*.
On that basis, the ROSCOs that own the 153s may offer them in some form** to bidders for upcoming franchises with a high diesel requirement such as Wales & Borders or East Midlands regional.
That said, with 769s, dieselised 455s (is 255 available?

) and even 230s, even with the electrification cancellations the market for self-powered units should be reasonably competitive. This will place a ceiling on how much is worth investing in 153s.
*= Has another 155 gone up yet? What odds on no further units being done, I wonder...?
**= A while back (i.e. pre-Northern franchise contest) I looked at the numbers of 153/155 vehicles and crayoned up a proposal to form a fleet of 3-car units (84, so 28 sets), though obviously that was never going to happen, not least because AIUI they're owned by different ROSCOs (Angel & Porterbrook IIRC, I know the 155s were transferred to Porterbrook from WYITA.