How about supporting functions like ABS as EXP in a better way than just as a function name.

Well, I am not sure that I agree with you here.

I mostly use the formatting to ensure a readable documentation of complex formulae, and to document how and why the functions work in the context of the spreadsheet.

If I just want to produce good looking math I can still do that in the normal ways like you have done in your examples, and it could much better describe the subject with as few or as many abstractions as required by the author.

However, when I produce a nice looking representation of an Excel formula in a spreadsheet, I want it to reflect the formulae/calculation in the specific cell, not some further abstraction. The initial suggestion where you convert the Excel-functions to equivalent math-symbols is fine since it improve readability, but translating actual cell-references does IMHO not help.