There was way more than two Dark-types in Gen II: Umbreon, Houndour, Houndoom, Sneasel, Tyranitar, and Murkrow. I say twenty because the Type with the lowest amount is Ghost and Dark(17-19 each), and that's including every non-Arceus pokemon in Gen IV. There's around 25 Dragons, give or take a few, and there was only a small amount of Dark-types in Gen II because out of the 251 pokes, over half were already dual-typed and the vast majority don't even fit the "dirty tactics" definition that is Dark Pokemon.
Once Gen V comes out there will be over 600 pokemon, so asking for twenty of a type isn't that hard to ask, but you guys keep coming up with types THAT FIT ONLY A SMALL HANDFUL OF EXISTING POKEMON, so they'll HAVE to create around twenty NEW pokemon of that type in order to balance out the PERFECT battle system that we have.
In addition, those weaknesses/resistances to your beloved Space-type make zero sense. Flying: space is a vacuum, NO BIRD/BIRD-LIKE THING WILL BE FLYING ANYTIME SOON, seeing as it takes tremendously powerful engines to get anywhere in space. Dark: space is already pitch-black, and won't/can't get darker. Electric: I'm pretty sure electricity isn't conducted by nothingness. As for those resistances, they can't even be propelled through space by their own accord.
You'll probably say "well, the Pokemon isn't space itself", to which I'll reply: It'll have characteristics of something flying through/living in space, so it'll look like this:
Resistances(if not immunities, even)
Ice(sub-zero temps, gotta survive travel somehow)
Dark(for reasons stated in a previous paragraph)
Fighting(pretty hard for something terrestrial to move in space, and the creature probably distorts gravity some way)
Ground(at the right velocity and proper size, it can crash through a terrestrial planet, a moon, and asteroid)
Rock(same as ground)
Flying(nothing of a Pokemon's size can just fly through space, 'cept Deoxys 'cos he IS from space)
Weaknesses
Psychic(the ability to stop it with mental power...even from far away)
Fire(a massive temp change is bound to confuse its body)
Ground(stopping the traveling object due to a higher durability)
Rock(same as Ground)
*note, Rock and Ground can be either/or, due to them being extremely similar
It all comes down to common sense, really, and there's no sense pretending that theyvadded new types to Gen V. We'd have seen that in Reshiram/Zekrom for sure if it was true.