Apologies TD I should have been a bit more specific with the 155 comment, and should have added a couple of these.
It was only due to the fact I'd seen 153 pairs around Bristol and if what was rumoured elsewhere that 2 car 150's weren't being cascaded it really wouldn't make much difference if the equivalent number of 153's turned up, albeit they were limited to the Bristol side of Southampton. There must be several 150 diagrams that a 2 x 153 could happily do. Whether that happens I suppose depends on whether
FGW▸ think they would be better off with the flexibility that the single cars would provide, and I'm not forgetting Melksham here either. All speculation of course until it actually happens.
If I'd remembered the 153 limitations in the first place I wouldn't have gone to the lengths I did wondering if a 153 cascade would 'allow' a complete 4 car Portsmouth/Cardiff enhancement, that will have to await shuffling the 158's again I would guess.
AFAIK▸ this requires another 2 off 158/7 to give the required number of vehicles, and I don't see those appearing from outside FGW, and to take them from other services would clearly reduce the standard there.
Mmmmm what about those 2 sad examples someone mentioned the other day that Arriva seem not to care about very much. I'm sure they would be far happier going to the seaside at Portsmouth.