A tag was created at that stage to facilitate continuation from that point. The entire delta from that point can be examined here. It appears that the major improvements to the client occurred before this time. The isolated nature of the game manager allows the other non-game manager work to be picked over with ease.
Correct. The client compiles with VC++2013 for certain, which supports the XP toolchain. The string_theory dependency will compile with VC++2013 if you use string_theory 2.2. If you prefer to use the latest string_theory 3.0, then bumping everything to VC++2015 is needed. VC++2015 also supports the XP toolchain. Note that I have yet to update my build system to string_theory 3.0, so this is not needed, strictly speaking.
But are we seriously debating a 19 year old operating system when Windows 7 is on the cusp of obsolescence itself?