I'd like to see four types of monsters / NPCs in 5E:
1) NPCs for interaction
Ex: Kings, questgivers, bar wenches...
These don't need combat stat writeups, just ability scores and skills
2) Monsters
Ex: Purple Worm, Orc warband
These are purely combat enemies. They use 4E monster format, because it's the easiest to use.
3) PC-like NPCs
Ex: Tenser, Mordenkainen, Warduke...
These are created using simplified and more flexible PC creation rules. These are major campaign persona. They can either be powerful neutral individuals, allies or major villains.
4) Unique, intelligent monsters
Ex: Individual Rakshasa, Succubi, Ancient Dragons
These are created based on a monster entry, but have access to spells, class abilities etc. that make them more like PCs.