It is trivial both to ban tabs and to bulk convert tabs to spaces in a codebase or presubmit hook. The other direction seems impossible. That means that if you

It is trivial both to ban tabs and to bulk convert tabs to spaces in a codebase or presubmit hook. The other direction seems impossible. That means that if you want to avoid a mixed codebase it is far easier to get to and stay at spaces only than tabs-for-indent, spaces-for-alignment.