Releasing Gray as a DS game doesn't make much sense, and making it for the 3DS would require a lot of work to be at all worthwhile, so I'm inclined to believe this. Based on that, I'd also expect to see the next mainline Pokemon release, a 3DS exclusive, to come sooner than usual; the standard seems to be about a 3 year gap between major releases, but I wouldn't be surprised to see the first 3DS installments even as soon as late next year.