The sixth generation will probably be an expansion pack generation like the second and fourth generations, but I hope it introduces 150 Pokemon instead of 100. Not to mention evolutions that aren't ugly as sin. That would make it a little bit bearable.
If we assume about 100 Pokemon and a Johto/Sinnoh style Dex there's a ton we can come to assume about Gen 6's make up:
X6 3-stage lines (incl. starters and a psuedo-legendary)
X18-20 2-stage lines
4-5 Alternate evos (incl. (possibly) 2 Eevee-evolutions)
6-17 Extra-evos (G.2 had 6, G.4 had 17)
No fewer than 10 legends
Although Gen 2 had 22 non-evolving non-legends there's been a trend against them in the last 2 gens, so those 1 stagers may be closer to Gen 4's 5.
There may also be:
A 2-stage ground/water Pokemon found earlish in the game (Wooper/Sheilos)
At least one 2-stage Bug Pokemon for early game (Ledyba/Spinarak/Kriketot)
A later game 2-stage Ground type based on a large African mammal (Hippopotas/Phanphy)
A 3-stage electric Pokemon found early in the game (Mareep/Shinx).
A 2-stage normal rodent found in the early game (Rattata/Sentret/Zigzagoon/Bidoof/Patrat)
A 2/3 stage normal/flying bird (Pidgey/Spearow/Hoot-hoot/Tailow/Starly/Pidove)
A 2 stage pure Grass family with some connection to the sun (Sunkern/Cherubi)
If they follow Sinnoh more, we may also see these (as opposed to Jhoto which didn't include them as they were more of a 'sequel' to Kanto's Pokemon):
2 2-stage Fossil Pokemon
A 2-stage cat Pokemon (possibly of normal type -Meowth/Skitty/Purugly/Purrloin)
A stand alone non-legend Grass type (Tangela/Tropius/Carnivine/Maractus)
A 2-stage Dual Grass type family, usually in the second half of the dex (Exeggcute/Cacnea*/Snover/Ferroseed)
*Obviously Cacnea is a pure Grass, but it gains Dark upon evolution, so like Tropius, it is a bit of an exception (Tropius being the only one of its group to be a dual-type)
And now that you all think I'm crazy and have put too much thought into all this, I'll add that it's possible
that cross-gen evos next gen may be largely or exclusively limited to Unovan Pokemon. Just a thought.
that we had... too much blue/purple/black. The amount of blue is unbelievable, and it's almost close to purplish/dark gray/black pokémon; go here
and check from Mime Jr. to Magnezone, it's almost insulting. You don't have it with B/W, and that's something I really loved about the designs.
-- Lol actually you could even go as far as starting from Ambipom or Cherubi...
Oh goodness, I thought I was the only one to notice this!