Agree with PVP, if you're thinking of using the Crofton park-Blackfriars route to avoid overcrowding (rather than the issue with interchanging), then don't bother - the trains are arguably worse than the Ginger line at any time after 7.45 until 9.30.

Unless of course, the delightful Thameslink in their wisdom think about using some of the rolling stock not in service now London Bridge is closed to extend the 8 carriage (or sometimes even 4 carriage!) trains on the routes that are running to ease congestion. But that might be just too sensible!