After I've read all comment in this thread, I think it't time for me and my speculations.
Eeveelutions: In my opinion, Sylveon may be either Dragon or Flying, or, if completely new type, then probably Rainbow or Light (and for the name, from what "element" is the "sylv" part? If from latin, then sylvestris means "wild"; silvestris mean "forest")?
Evolution and pre-evolution form other old Pokémon? I practically agree with Farfetch'd and with all the #12x Pokémon from Gen I (Mr. Mime, Sycther, Jynx, Electabuzz, Magmar, Pinsir, Tauros and Lapras) - it'd be interesting, if all of them have a "complete" both pre-evo and evo. Then, some of you say, that if Pinsir, then a Heracross too - why not?
It'd be nice, if a Weezing would have an evo, it could look quite 3D-symetrical Koffing with four heads connected in the middle (something like Metagross concept).
Then an Exeggutor evo finally with arms (it can have some branches with "coconuts fingers").
I thought about Victreebel, too. When a Gloom has an alt evo in Gen II, why not its "counterpart"?
Next, something like Nido-line - two "same" Pokémon with completely different genders and evos, maybe.
Evo for Parasect? Mabye. Golduck? Maybe. Primeape? No. Tentacruel? Maybe. Seaking? Yes. Starmie? Maybe.
But interesting would be, if we have an evo for Dugtrio or Dodrio with 5 heads/bodies. :-D And pre-evo for Kangaskhan.
From the 2nd Gen maybe evo for Sudowoodo, Magcargo, maybe Stantler or Donphan.
From the 3rd Gen maybe a "counterpart" for Absol (named like some corruption of "Cataclysm").
The idea with some Pokémon like "connector" of other two Pokémon (Luvdisc-Alomomola / Kingler-Crawdaunt) seems unlikely, but it may be interesting.
On the other note, if we can make some Pokémon to delete, I vote for Rhyperior, Lickylicky, Tangrowth, Yanmega, Spiritomb and other "unsuccesfull" evolutions/designs.