Nothing in the race description implies that a revenant loses the requirement to sleep, breathe etc. I'm guessing that you're getting tripped up by previous editions' beings with the same name and thought that this 5e version was undead?
Yes, they are in previous versions. And 5th (look it up: Monster Manual, page 259). And other games that have undead. And folklore. And movies. And television. And books. And comics (Crow, anyone?). And... You get the idea. The bottom line is that most people with even the tiniest bit of knowledge about this sort of thing are going to assume undead. So, if they aren't undead, using the name "revenant" was just plain silly. I suspect that they really
are supposed to be undead (again, see MM, page 259) - Mike just forgot to note it.
Ignoring the whole undead thing, for a moment, though, the sub-race is badly balanced, since there was never an attempt, in the player's book, to balance the race-to-subrace power ratio between the various races. It wasn't really needed, at the time. This wasn't a serious problem, originally, as long as the whole package worked, but it does become a problem when you start replacing one of the two parts with something else. In math terms, if A + B (race one) more or less equals C + D (race two), you can only change both B and D to E, and keep your balance, if A and C are more or less equivalent (which they very much aren't, for D&D's races, some of which don't even have a B or a D). In less obscure non-mathematical game terms, add revenant to an elf or dwarf and you still get most of the parent race's goodies. Add it to a human and all you get, from the parent race, are the two ability score points (which
everyone gets) - nothing else. I'm guessing that this is why half-elves and half-orcs got left out - Mike realized that the lack of sub-races created a problem for them, so a different system would have to be used. He couldn't just do what he did with humans, or they would look pretty much the same as humans. But he couldn't let them keep some of their abilities, or humans would look ripped off. So, no half-elves or half-orcs, "for now." But he probably figured that he couldn't really ignore humans, since pretty much everyone pictures revenants coming from human stock (again, the Crow - not to mention numerous MM pictures, from various versions - probably contributes to this image).
The rules, as written, are also asking for trouble, within the game. In campaigns with high attrition, a PC group could quickly turn into a pack of revenants - unless the DM lets only one player do it, in which case accusations of playing favorites are inevitable. A few restrictions as to the sort of situations that create revenants, the sort of people who become revenants (probably linked to willpower, alignment, etc.), and so forth might have helped here, but I guess Mike didn't have time to add that to his three page article, over the course of two months.
I also see possible trouble with "Wolverine syndrome" - i.e. characters in stories with regeneration always seem to get abused the most, 'cause... well... they can be (without ending the story). In this case, I can see that, at least in some cases, the revenant character is going to end up coming back from the dead on a regular basis, either because he is a tempting target for the DM or because he gets used as a 10 foot pole by the rest of the team or because he knows he is unkillable, so, you know, what the heck? In a game with less combat and other regular life-threatening issues, this might be less of a problem - but in D&D? Anyway, this is not exactly a problem with the article, I know, but it is a possible problem with the whole idea. A problem which, again, was not addressed, at all.
In all, it seems to me that this suffers from a typical UA problem: interesting idea, weak implementation.
