Kamala’s problem is that she’s not eligible to be President so if they try that route there’s going to be an army of lawyers creating a fog around the whole thing. It will be a mess.
The only "eligibility" Biden and the Dems required was her race and gender.
The issue with that idea is that the qualifications for President and VP are identical according to the Constitution. So if she is in the office of VP now, it is implied that she is eligible to be President.