The best I know is that in theory the timetables for 2018 have not been finalised.
The Forest Hill Society has argued for the reinstatement of evening and weekend services either to Charing Cross, or on the Thameslink line. We believe this is preferable to having reduced service in the Thameslink core because of lack of demand for long distance services outside peak hours.
Unfortunately the tendering process tends to focus on peak services, where there is little opportunity for South Central/Southern services to use the higher level station at London Bridge.

If anybody does hear anything more definite then it would be good to share.