It's implied that the new games will take place in an entirely new region, it says in the trailer, "Explore a dramatic new world!" Also, in Pokemon X/Y, there is a traveler in a hotel that says "This region is nice and all, but you should really check out mine! Where is it you ask? Well, I can tell you it isn't Kanto, Johto, Hoenn, Sinnoh, or even Unova!" Not his exact words but pretty close, I am not making this up, look it up online if you want.

So there is an extremely large chance these two new games will be in an entirely new region.

Anyways, I am totally pumped for this! Saphire/Ruby/Emerald were definitely my favorite Pokemon games of all time.

http://cdn.medialib.officialnintendomagazine.co.uk/screens/screenshot_62410_thumb_wide930.jpg (Unsupported image host)

http://cdn.medialib.officialnintendomagazine.co.uk/screens/screenshot_62413_thumb_wide930.jpg (Unsupported image host)

EDIT: Here are screenshots of this particular traveler implying a new region. It's pretty obvious he is, since he tells you straightforward, so I have a pretty good feeling that the new games will take place in an entirely new region.

http://1687fa34097574f11013-f010928b0f6482a6479792d4809b5ba0.r36.cf1.rackcdn.com/60b09728416ace0b26aa24c7266007bfbfcc35cb.jpg__576x480_q85.jpg (Unsupported image host)

Here it says "Explore a dramatic new world!" which also implies a new region. Trailers of remakes of Silver/Gold and Red/Green have only said "Come revisit the region!" This trailer, however, invites us to explore an entirely new world.