Wouldnt they be used for the western Extention of the Heathrow Express service to Reading. Assuming they use the current Heathrow Express rolling stock going to Paddington.
You beat me to it.
As yet, nothing has been decided about how the Reading - Heathrow service will be operated and in what form it'll take.
Options would include...
Part of the GWML franchise (i.e. currently GWR)
An extension to Crossrail
A stand alone service (possibly operated by HAL, the owner of the Heathrow Connect 360's)
An extension to HEX (what happens after 2023 though???)
Development of the Western rail link to Heathrow (formerly WRatH), is already in process, with the various consultation processes complete. The formal planning application process commences early next year (a few months time), with construction due to start in about 18 months from now (early spring 2017).
Opening date is slated for late 2021 (6 years time).
A decision on what service is to be operated on this new line, will have to be made in the next year or two.
Are there enough 360's to match the expected diagrams for the proposed frequency?
If the suggested extension to Oxford is included, surely that would rule the 360's out on fleet size?