I was just about to post this. Read it over at Collider.com who got it from the link you posted.
I say: COOL! I love what 3D does to movies. To me it doesn't matter that it will be the only HP film(s) in 3D because you can always choose to watch it in 2D and the DVD's will be in 2D just like the others. It's just a way for them to pull in extra revenue, as Avatar has made so much money.