Bucks Railway Centre or Epping-Ongar seem suitable rest homes. At least there should be D Stock running for many years on the main line.
All remaining nine cars of A stock have a buyer lined up; it is not for preservation. The D78 trains require some further works but it is possible that one may escape before the end of the year.
TfL and the LT Museum did an unbelievably phenomenal job of running steam on the Circle for Met 150, and continue to do so on the Met steam days, but costs and logistics are spiralling, particularly with the SSL resignalling and automation.
Readers should be pleased to hear that there is one final soirée underground planned for next year. Final details are still being worked hrough but it will be to mark 150 years of the Metropolitan District Railway. This is in addition to the usual above-ground festivities. The latter are good for at least another 3-5 years as resignalling progresses, but this will be the last opportunity for the former as the top side of Circle should be ATO by the end of 2018.
When on the Jubilee line I’ve passed Neasden and Stratford Depots and they always seem rammed with trains, particularly the former. So, if they can have all of those trains out of service while still running the full Jubilee line to timetable surely they could spare four or five for the Island Line?
They would be a significant improvement from the current trains just under sixty years older!
You're completely misunderstanding the logistics of running a railway operation. Traditionally, the busiest times for the Tube have been during the morning and evening peaks, requiring more trains in service and introducing the concept of an "inter peak stabler", I.e. a train that returns to depot in between the peak periods. This down time is used to carry out maintenance tasks on these trains - indeed, in some cases maintenance has been deferred to eek out additional capacity during the peaks.
A number of trains will also be standing spare to allow for swift changeovers if anything goes defective, whilst the rest will be on heavier maintenance which couldn't be done without significant service reductions.
There are very few "spare" - as in could be released for other use - trains on the Combine, and certainly none at all on the Jubilee, irrespective of how many you see in depots off peak.