There is currently 4 per hour off peak Thameslink to Brighton, but from Dec 2015 there will be 2 Thameslink to Brighton and 2 Thameslink to Gatwick/Three Bridges calling at Purley, Coulsdon, Merstham and Redhill.
One assumes that the other two Thameslink to Brighton services will become London Bridge to Brighton to provide additional capacity when the core shuts down to London Bridge. Whether the London Bridge train will be the all stations south of Three Bridges or the fast service I don't know.
Redhill branch will lose both the Arun Valley trains and the Tonbridge/Reigate services to London Bridge so going from 4 trains per hour to 2 trains per hour off peak to London Bridge.
The Arun Valley trains will go down the quarry line and Redhill will get a new alternate Reigate/Tonbridge service that will go fast to East Croydon (unlike the London Bridge trains which were all stations) then Clapham Junction and Victoria.
This should improve reliability into London for Redhill but loses all connections from Redhill to the coast during the day.
That is off-peak only as details of Peak services are scarce for Jan 2015 onwards. The changes in off peak suggest there may be major changes during the peak.
So does Redhill go down to 4tph off-peak from December 2014?
2tph Victoria to Reigate / Tonbridge
2tph London Bridge to Horsham
...before, from December 2015, the Thameslink (Bedford) to Three Bridges service restores the 6tph? Then at some point in the future the London Bridge to Horsham train also comes from Thameslink (Peterborough).
Isn't there a minimum specification of 6tph to Redhill in the Franchise Agreement?
Connectivity south of Redhill doesn't seem great if that is to be cut from 5tph to 3tph for a year. Even after that, 1tph Gatwick (FGW), 2tph Three Bridges and 2tph Horsham isn't a great offering.
Does the off-peak Reigate / Tonbridge service run to Victoria? Doesn't that defeat the object of removing crossing movements at Stoats Nest or Windmill Bridge? The Thameslink interactive map on the DFT website suggests faster journeys to *London Bridge* from Reigate by eight minutes.
When does this become clear? - eg publication of a draft timetable like Southeastern have done