I read elsewhere today that apparently GWR might be now taking on the TfW 158s. If true I don't know what that would mean for the 175s...
There are multiple rumours, but I am guessing some serious contingency planning must be on the table by now. The first 175s arrived over 18 months ago, and they just don't seem to be fixable to the point of doing 1000 fault free miles.
There have been talk of the TfW 158s, even some of the TfW 150s (others are virtually out of miles before expensive overhaul).
But there were supposed to be enhancements, Cornwall metro, some lengthening of Bristol area trains, Okehampton, Portishead, Restoring 4 or 5car on Cardiff-Portsmouth etc. If 175s don't work need extra other stock for this.
The frustration is that there are spare EMUs, but because of the lack of extending electrification, they are going for scrap, whilst the 34-40 diesel units struggle on, but have no replacements on order.
In blunt terms, currently policy is 175s or nothing, and with 175s continuing not to work, nothing is accidently becoming the outcome, but continuing nothing with a fleet approaching 40 years old is not practical, hence the ideas of scrabbling around for whatever can be got.