It's not bad. But there's quibbles.
First, there's the problem of the player getting "good instruction" for what is possible. I've seen this at work in the 5e playtest: having the ability to do anything can leave you paralyzed with options, unable to think of what you should do in any given situation. Not every player has a problem with this, but I've seen a lot of people just shrug and do some default action over and over again and get a little bored with it because they can't see what they can do.
The other side of this is a DM getting "good numbers" for what is possible. 4e's Page 42 could, slightly expanded, be a great basis for an entire RPG built entirely around what Monte is advocating. 5e doesn't have something like that yet, which means the DM gets her own special version of the analysis paralysis: I don't know HOW to adjudicate this so that it has some effect without having ALL the effect.
Balance concerns figure into this, too. Relying on the DM means subtle personality quirks and rules opinions can drastically swing the play experience. One DM things wizards are teh overpowerdz, so she uses her powers of interpretation to nerf every spell into ineffectiveness (the "Charm Person makes them your friend, but this goblin loves to stab his friends!" kind of DM). Another DM thinks wizards SHOULD be the most powerful of all ever, so she uses HER powers of interpretation to make wizards always the best choice (the "Charm Person gives you a loyal peon for life, and no one else can convince an NPC of anything" kind of DM).
You can give DMs all the advice and guidance you want, and not eliminate this problem, because much of it lies in the realm of emotion and opinion, and not fact and reason.
And the absurd endpoint of the concept is to not have any rules at all because all we need is a player who says "I do X" and a DM who says "Y happens," and uses some half-arbitrary criteria to decide on success or failure.
People need hooks to hang their characters on, and DMs need hooks to hang their arbitration on, and no amount of text in a rulebook is going to train a good DM. Only experience does that. Experience using those hooks and examples and rules as training wheels to get to the point where they can confidently ignore them, if they want to.
A game consisting of a PHB that says: "Do anything you want!" and a DMG that says "Figure out what happens!" doesn't give me enough hooks to hang anything on.
To a certain degree, this was a problem with my 4e experience. Lots of places where the rules told me to do it myself, and, as a result, I had no real idea what to do.
In other words, it's a great Rule Zero, but we're gonna need more than that (even if just a little bit).
