The idea is not necessarily bad, but would almost certainly succeed in destroying everything that made Rugrats stand out as one of Nick's highest rated and original shows.
The imagination and adventures just wouldn't be up to par with the original style that made it unique (esp when veering too far away from the childlike innocents). This is really only unless the adult versions were on their couch all day getting high, in which Nickelodeon would not air it as they do not even have an afternight adult themed schedule.
It's like rebooting Pokémon, but from the perspective of an older retired Ash who no longer train nor travel. Sure there may be some arguably good elements to it, but ultimately what made Pokémon the show great is greatly diminished (if not eradicated) to the point of near complete redundancy.