The way I see it, they will never be able to pull off a 5E rewrite that doesn't turn into a total financial disaster or public relations nightmare.
But that's not to say the idea of a 'monstrous heroes' book is a bad idea. If it's done right, I think such a book could be a solid hit.
I'm thinking the best chance of success would be with a monstrous PC-themed splatbook in the same vein as Volo's Guide to Monsters and Tasha's Cauldron of Everything. Let's call it, I dunno, "Thar's Guide to Orcs and Goblins." Its scope: to expand upon the different races and subraces of goblins, bugbears, kobolds, trolls, and so forth.
First, they would need to sort out what it means to be "monstrous" in the game setting, and steer clear of outdated (and frankly, lazy) tropes like 'all trolls are bad guys, and all bad guys are evil.' They're better than that. And they can't use real-world cultures as templates for non-human creatures: I understand the temptation, but there's no polite way to refer to a real group of people as non-human. So Step One would be to flex their world-building creative muscles to create new cultures, names, and mythos completely from scratch.
Since this is a player-facing splatbook, there would need to be lots of new crunch for players: new magic items, new weapons, new feats, new mounts and familiars and spells, and new class options. If they're feeling extra-ambitious, and if they really want to bait that hook, they could throw in a whole new core class like Marshal (for the hobgoblin fans).
But DMs buy more books than players do, so they would need to write in lots of DM-facing materials to draw them in also. Instead of that weird "Orc Wars" mini-game, they could put in some fresh wargaming rules for mass combat and siege weapons. There should be plenty of new lore, like pantheons, new history, factions, and NPCs. There would need to be new maps of the Broken Lands, too, redrawn to fit whatever default campaign setting the 5E rules are publishing that year. Conversion notes for inserting The Broken Lands into Faerun, Eberron, Wildemount, and whatever.
I think it could work.
But I have to stress that this project would need to be a complete rewrite. The Orcs of Thar 5E would never work. Imagine what would happen if they just updated the mechanics and replaced the offensive text and images, and put out a sanitized version. Players new and old would take them to task! Twitter would explode with righteous fury, and shareholders would run for cover. No, the "silly D&D book" experiments of the 1980s all failed, and this one failed the hardest...they should not attempt it or anything like it, ever again.