Here's what I'm looking at http://www.allbabynames.com/BabyName/Latin/Syl.aspx
Meaning: short form of various names meaning "forest" Expression: People with the name Syl tend to be idealistic, highly immaginative, intuitive, and spiritual. They seek after spiritual truth and often find it. They tend to be visionary and may inspire others. If they fail to develop their potential, they may become dreamers, or misuse power.
May somehow be tied directly with the Dream World.
Also it's base word in the French version is nymph and German is Feel.... maybe Happiness could take a greater role in this version than just the side-quests and mini-games we know it to be now.
They'd use it as a selling point from day 1 if there was a new type.
Because the fact that this game is the first main series Pokemon game entirely in 3D with full animations is not a bigger and better selling point?
If they released both types of information at the same time or close together, one would overshadow the other. It's best to disperse it to make each tidbit that much more exciting and to maintain hype. If you release all the big info right away, the hype kinda dies with the release so far away.
And a new type isn't that amazing of news. It's pretty cool, but nowhere near as big as an entire change in the design of the game.