The pink elephant in the room (literally) is the GOP saying nothing about this and not demanding an independent prosecutor, while a corrupt democrat is on the verge of the presidency.
I don’t think an independent prosecutor would speed things up, but it might take some of the politics out of the decision to charge or not charge.
Hard to imagine a case with more political ramifications than this one. On the merits, it appears obvious to me that she should be charged with mishandling classified information. There is no “I did not know” or “it was not marked.” That case seems rather simple - it either is or it is not classified information. If it is, she and those who sent the stuff to her personal email server are guilty.
The corruption or pay to play investigation will take much longer. At some point they are going to have to recommend charges because the longer they wait the worse it becomes politically.
There is also another concern on the part of political appointees and career attorneys at DOJ - what if Trump is elected and they stonewalled or crushed the investigation for political reasons? They might be in trouble.