I understand the sentiment, but I do not come to the same conclusion that of increasing accessibility via offering more features in unfree proprietary software. The intended consequences of this were publicised by US Justice Department in their uncovering of Microsoft’s memo labelled Embrace, Extend, and Extinguish which outlines how this eventually leads to less, not more, accessibility.

That aside, Microsoft Windows already supported ZIP which is an open standard. The addition of RAR, which is a proprietary unfree standard, is actually less open.