I absolutely do NOT want monsters available as default. That is purely a setting-specific, playstyle, group-to-group preference. Allowing monsters as PCs has no business being imposed upon D&D. Another game system/line that is created with that assumption built in? Fine. But not D&D.
I am not objecting to an optional [appendix?] in the MM with guidelines to using humanoid creatures "Small" (matching halflings) up to "Large" size. Given examples could include: Small: Pixie, Goblin, Kobold; Medium: Hobgoblin, Orc, Lizardmen; Large: Bugbear, Gnoll (though I continue to be baffled by the attention and adoration given to savage-bordering-on-insane hyena-men?!?), Minotaurs (Krynn, anyone?)..."Half-Ogre" (for such settings as use/allow that sorta thing)...maybe something like Nymph or Siren to add in some Mediums that aren't "evil goblinoids."
This option also has THOROUGH guidelines and advice for using such creatures, including the subtle prejudices to abject panic and horror that a party "with a gnoll" ??!? attracts walking into EastBumble Hamlet farming village.
If you want to play "Beholders & Dragons" that is certainly your prerogative, but I don't want to see page count wasted on it in the MM or anywhere else for that matter.
All hail the One True Way