There are insiders who post here that know far more than me though, I'd expect someone will be along before too long...
Here sir! Been busy watching the football. Wish I'd had that 4/1 on England win and both teams score.
Not much to add to what has been said. But I will anyway.
1) Borough market isn't the main bottleneck for Charing Cross services - trains can be timed to follow 90 seconds apart, and regularly beat that. The bottlenecks are Charing Cross platforms, Thameslink trains crossing at Met Jn and Spa Rd Jn, and SE trains crossing from slow side to Charing X or fast side to Cannon St on the eastern approaches. All being fixed save for the CHX platforms.
2) there was much argument about providing point work between the TL lines and Charing Cross lines both at Met Jn and east of London Bridge. It will be installed but only ever used for planned engineering work, or in extremis to deal with a major failure. They won't be used during most disruptive incidents, as it will spread delays from SE to TL or vice versa. London Bridge will have four separate railways: Southern into platforms 10-15, SE CHX into 6-9, Thameslink on 4&5, SE CST 1-3. There will be no interaction between the services at all, indeed they will be controlled by 3 or 4 different signallers (tbc).
3) the new viaduct is for CHX services. As a by product it gets a line speed improvement which will shave a small amount of time off all services to/from CHX. The main benefit of this is slightly improved junction clearance times at Borough Market and Met Jns.
4) it won't just be a new station. It will be
the best station in the country, arguably Europe (from my experience).