Do the mark 4s and 197s have anything to do with TfW's plans for releasing 143s/769s? I thought the plan was for 170s, 230s and 153s to come in and displace 150s from non-valleys routes so that virtually all TfW's 150s become concentrated on the ValleyLines which, together with the 769s if they worked, would replace the 143s.
This would mean the south Wales metro routes being covered by 57 existing units (170s, 150s and 769s) which seems likely to be enough units to cover the work given that the planned Stadler fleet (231s, 398s and 756s) is only 71 units (a mere 14 more than the existing fleet despite the massive frequency uplift planned).