This is infeasible, and what does it mean to reject something in a written document?

I don't understand what you're trying to accomplish here: you're arguing against an established convention in a sector of the market which you don't have experience with.

The upside if you're successful is that I don't need to type an additional 'M'.

The downside is that it requires enforcing a blanket standard on an industry, rather than letting it converge over time to an unambiguous standard.