The only pre-evolutions I'd like to see (NATURALLY, in wild, without incense) are ones for some gen 5 pokemon
It's really absurd how long you have to carry around Rufflet, Mienfoo, Vullaby, & Pawniard (& probably a few others but those take the cake) before they evolve. Even in their original games, with their exp system and placement in the game, you are still very likely not getting any of these evolved until after beating Ghetsis. So it's even worse now, where you can get something like Mienfoo before gym 2 but will be carrying this same pokemon until at least the climax before it finally evolves.
Pre-evolutions aren't the best solution, but I doubt they're ever going to retcon in mid-level evolutions so its the best shot they got and give an actual sense of progression. And maybe give a slight BST boost to the former-first stages to help make the wait a little less bad.