The problem I see is that we're going to have a half dozen monster tomes that largely reprint the same core monsters (goblins, dragons, giants, vampires, etc) with just slightly variant lore along side of specific monsters for the setting, you'll have unique variations of the same types of monsters (goblin bandit in one, goblin infiltrator in another) or you'll split the monsters around several books (vampire in the Ravenloft MM, giants in the Eberron, drow in the FR). No matter how you slice that, you're buying multiple books either with repetitive info or the core info across multiple books (which was popular during 4e when they split the base classes and monsters over different PHBs and MMs).
No. One core book of basic monsters and let setting books deviate as needed. It's not like D&D settings share 90% of the same monsters anyway. I can't feel bothered that someone is whining "you got Forgotten Realms lore in muh Eberron". It's a game of imagination, pretend it's not there.