I actually have a certain ammount of faith in this theory. I doubt it will ever be confirmed, but it seems likely it was considered.
Of course, Marrowaks can give birth to Cubones, but the details of Pokémon evolution are vague- there seems to be a magical element to it in a lot of cases. I guess the skull is "incorporated" into it somehow and it cannot evolve into a Kangashkan, it has become a marowak instead.
The only other way I could think of explaining how every Cubone has its mothers skull was by saying marowaks always die in childbirth. But in red and blue it is explained that team rocket killed cubone's mother.
Missingno is data created to store your name once the old man teaches you how to catch Pokemon. NOT a failed Pokemon, as many people believe.
Missingno was a placeholder because there needs to be a certain ammount of data for every option but there were only 151 actual Pokémon. So each one was a Missingno until it was programmed with its actual data, and the remaining spaces are still fillied with Missingnos.
However, some of the Missingnos that can be caught do odd things- for example, evolving into Kangashkan. This implies that a Pokémon was programmed which evolved into Kanga, but was then removed from the game.