I think a majority of people ask for a Kangaskhan pre-evo, because of the child it carries in its pouch. When you breed a Kangaskhan, you end up hatching a Kangaskhan with a baby already there. That hardly makes any sense. Even though the PokéDex entries are never followed literally in the games, it would still be nice for the sake of consistency and logic to hatch a pre-evolution of a fully formed Kangaskhan.Sadly, it actually almost needs its own evolution instead. A Pre-evo is what we always wanted for it, but in my opinion it would be as useless as chingling.
That being said, an evolution would be awesome. Looking at its base stats, an evolution of Kangaskhan could be a real powerhouse both in-game and in competitive play. With a possible secondary type and a good movepool (which it pretty much already has), you're just asking for trouble [in the best way possible].