Personally, I don't see the point of the secret Key.
It should be like Castform
Sandy weather: Spin *to blow sand away*
Sunny: Heat
Hail: Frost
Rain Wash
Foggy: Cut
I mean, the true rotom looks like castform
I don't see any connections with these two.
Bad Idea, anyways. If it did work that way, than Cut Forme would be impossible to use PvP, and all of its attacks would have their accuracy cut in half. Plus, you would proabably need a hold item, as Gamefreak hates Paradoxes (Why wouldn't it work in D/P?).
That is why Eevee doesn't become Leafeon via Leaf Stone and why you can still get Egg of Pokemon, like Snorlax and Wobbuffett, who got Pre-evolutions in 3rd/4th Gen. Also, that's also why you can still get Male Gardevoir and Female Glalie.
The only 2 Continuity Mistakes Gamefreak has made are these:
-Piloswine could get Ancienpower via Breeding in 2nd and 3rd Gen.
-Lickitung could get Rollout via TM in 2nd Gen and via Move Tutor in 3rd Gen
If you notice, those are the moves needed in 4th Gen to evolve them, yet they could get them previously and NOT evolve.
Back on topic, The Rotom formes can at least be used via Local Wireless Battles, but thats about it.
But as a side note, the people of Pokesav.com created an AR code that allows the use of the new formes on Wi-Fi.