I always thought Windsor would have made a good branch for at least 2tph Crossrail. It would have needed just a single dive-under at Slough. Good intermediate turning point (especially now Slough is no longer turning slow services) - plus offpeak, counter, weekend/leisure demand, some business - would be well used. And eliminate some diesel running. Nice station too - the Crossrail unit would be halfway to Slough
Western, I can only see frequencies. Things being jigged around to gradually extend things west - be it more service to Heathrow or adding the odd Hayes or West Drayton teerminator, westwards from Paddington/OOC, if stopping patterns allow. It should be more of a metro for all of the stations. And a lot of TOD will see crazy demand, I think - plus a return to LHR business as usual.
Eastwards - there have been studies and I think there is a preferred extension to Ebbsfleet/Northfleet recently published. It involved more platforms at Dartford and taking on a lot more of the east of Dartford services, as I recall. Gravesend, I can't remember - it has the bay for 2tph at least. But I certainly don't think east of there is planned.