You're never going to need to do that, if the MM contains sample characters. They don't need to be many, and they don't need to be for all humanoid creatures. For example, a sample 5th-level Drow warrior and a sample 7th-level Drow priestess, and you already have what you want: two versions of ready-playable Drow "monsters" (if it were for me, I'd also add a 6th-level Drow Wizard in between).
But with the monster entry in the MM also containing a description of the Drow race (and BTW, races ARE templates!), all the applications I described previously (using Drow as PC, creating a Drow NPC party, or just being able to use Drow at roughly all levels up to 20) would be possible.
There aren't that many iconic humanoid monsters that need this treatment: drow, orcs, hobgoblins, tiefling, duergar... maybe goblins, kobolds and a couple more, but hardly more than a dozen. I don't think this is an issue of space, and if it is then just do it for the top 4-5.