What limits charging is the power that the cells can accept, not the fuse. (A battery cell can accept less power input than what it is capable of getting out; whereas the fuse does not care which way the current flows.)
A fun calculation : taking the 'old' fuse limit into account and a low pack voltage for the 85kWh battery yields a maximum power through the fuse at 350V * 1300A = 455kW. Clearly, that's not the bottleneck for charging !
[Edit :] As randompersonx said, the 1300A rating is burst, not continuous, so my calculation is moot.
Anyhow, I do not believe the 'old' fuse is what limits supercharging at 120kW, but I do not have any evidence to back this up.
Charging is limited by the parasitic energy dissipated by resistance internal to the cells, which tends to heat them and cause chemical modifications such as plating of the electrodes, if I understand it right. So dissipation in an external switch should not be relevant to the warming of the cells' innards, whereas active cooling of the pack is very relevant. A superconducting battery could presumably be charged at an arbitrary rate.