Hmm, well there'd be 21 317/5 or /8s to replace excluding the /7 demonstrator, quite conveniently there are 21 321/322s available from GN and Northern. If that's a likely outcome for their relocation then it'd make sense, but it wouldn't add any additional capacity - I'm not sure what scope or requirement there is for that on the West Anglia side, but even if all those units are moved to serve Liverpool Street (I had originally assumed some were going to Scotrail for the 320 conversion but perhaps the London Midland 7 are sufficient for that?), it just seems unlikely to me given the current high demand for rolling stock that all the effort involved with that cascade would achieve nothing more than scrapping 36 year old units to replace them with an equal number of 28 year old units and provide a negligible improvement to passenger experience, journey times and reliability, without carrying out an extensive refurbishment which they could still have performed on the 317s anyway. I just get the feeling that the DfT and/or TOCs involved would want to get more out of such a deal than that, such as an actual increase in the number of available units - hinting that perhaps not all of the original build 317s would be scrapped, and if not, what then?