I would really like this.
I can’t think of why not off the top of my head, though things can be harder to code in reality than you’d imagine sometimes.
It’s not like you’d have to have dragons spawning in noob river or anything, but even say 3 or 4 different mob types (appropriate to the area) randomised from each spawn point would go a long way to making the world seem more real, alive and reduce the complacency that develops once you memorise the spawn-points.
The rare chance of an uber version (miniboss) of each creature type spawning would be cool to experience too. Say, something with a slightly different coloured skin or just slightly larger so you’d know it’s a special one. Maybe these could drop something a bit better than the regular mobs too.