I would have thought Bicester (either) would be a goal. Oxford of course is well-served on the GWML. Banbury and beyond is probably more marginal, but the LHR and Crossrail connection I'd think popular.
Unless the idea is now to be fully metro - i.e. 4tph stopping to connect in with Crossrail.
Unless the idea is now to be fully metro - i.e. 4tph stopping to connect in with Crossrail.