Earlier quoted context omitted.
Whether this "Promise" is actually worth much depends on much more than just the question of its legal legitimacy, as you'd have learned if you actually bothered to read the articles. But, as far as that particular issue is concerned, as the techrights article points out, "It may become legally binding ... if used as a challenge in court. But of course it does actually need to be tested in court /first/."
Yes well, I could have used the same argument against the GPL back in the day. And really, I don't need to read through an article by someone who declared the Mono project "dead" a few months ago because he couldn't find the SVN repository. Or spams Reddit endlessly. Not to mention the years of insults and ideological attacks on various FOSS people. In any case, you might want to look up the legal term estoppel .
So please stop repeating estoppel meme, it is nonsense. Also, attacking all people who show the world truth about Mono shows you have no arguments. Reddit was spammed by Mono pushers who were impersonating other people.