No. Absolutely not. The books do not need to tell me how often races should appear in my game. Put the races in the book, let ME, the DM decide what's going to be in my world, let ME, the DM decide what my players can or cannot play.
I do not want to have a little "Mythic Rare" symbol next to ANY race that says "these races are rare, you have to pay $50 to buy them on ebay." No really, D&D does not need a rarity system, it lends NOTHING to a game. Tell the DMs that THEY can control what is in THEIR game. End of story, we don't need to go any further than that.
You cannot on one hand put the DM in charge, and then run around telling them what they should or should not be doing. Especially if it's some abstract designer decision of "oh, Dragonborn are rare in Mearls mind, so they must be rare in the books and everyone else's campaign."
The whole article is about accepting other people's views of differing ideas of fantasy, except when it comes down to it, they really haven't accepted other people's views, and are acting like they are by foisting their views on everyone. How is that a solution?
If all races are default "0", then DM's can assign their own rarities to them. There is absolutely no need to attach rarities to races, it will be the first thing any DM with any kahones will ignore. Tell the DM they're in charge, give the DM options, and leave it at that. If people are offended by the fact that players can, and want to play more than the "core four", well tough beans! There's a lot of definitions of fantasy, if that DM doesn't want to allow those races, they can do so without the books telling players that their racial choices are less valid.