I think it would suffice
if it starts at the beginning, like when 6e gets published (or if a section like this was put into each monster in the Monsters of the Multiverse book, which I think is going to replace the MM?). Eberron came late and the first MM (either for 3e or 3.5) didn't reflect Eberron's trends. You had to have read the Eberron books, or at least be familiar with them, to know that their orcs are different.
But imagine the 6e MM, where the first time you read about orcs, you get the following:
* Generic orcs, perhaps writing them as tending towards being very physical but not inherently evil--more "big emotions and very demonstrative about them," that sort of thing. At least that's how I see orcs; I dunno how 6e will write them.
* Gruumsh's orcs, who are seized by religious fervor and because of that, are incredibly violent and warlike, as Gruumsh demands constant bloodshed in his name. This would be generic, in the sense that it can go in any setting and isn't tied to one published setting. But it's not the norm; it's just one group of orcs.
* NV2's orcs, unless the generic orcs above are the NV2 orcs.
And possibly, depending on what settings 6e wants to support:
* Orcs in the Realms or Greyhawk, who are mostly low-threat raiders, mercenaries, except in the cases of Obould Many-Arrows or the orc nation of the Pomarj, which are like this.
* Orcs in Eberron, who are druidic mystics who fight aberrations.
And each section would likely only need a few sentences to start with. This would take up a lot of room, yes, but honestly I think they could make it fit. Of course, by the time this hypothetical 6e comes out, they could decide to have a huge online section, or sell extended pdf editions that have all the info they couldn't fit in the printed book.
And this assumes that orcs (and other playable races) are even in the MM to begin with. If there's an extended NPC statblock section and a list of racial templates (akin to the one currently in the DMG), and that's the only place where orcs and other humanoids are listed in the MM, with the idea being that you just slap the orc template on the Commoner or Noble or Thug or Warlord stats, then that'd be fine by me.