EVERYTHING is a franchise these days. Until it flops, and then it just becomes fodder for a reboot 3-5 years down the line.
But seriously, everything that ever comes out today is a multi-platform, multi-media, multi-chapter, multi-multi deal, whether it's a book, a comic, a TV show, a movie, a video game, or all of the above all at once. Everything. Pixar was the one bucking the trend by continuing to release new material every year, until they put 3 sequels on the schedule (one of which is coming from the biggest cross-platform merchandising hit to land since Disney Princesses), so it's not even true about them any more. Given that, I can't really find it in my heart to criticize DreamWorks for doing the same despite my sense that something's getting lost in all the sequels, prequels, fill-ins, reboots, restarts, re-visions, alternate universes, and rehashes of the same stuff.
That being said, while "Yeah, we always planned this as a multi-part epic" is standard operating marketing-speak from Jeff Katzenberg,
HTTYD seems like the property they have most able to support it. As Shawn said, it's a property that's coming from a multi-part series of books (and there goes that franchise thing again), so there's plenty of source material to draw from/be inspired by. I'd say it has a better shot than
Kung Fu Panda (which
I liked quite a bit), and definitely don't think it's going to hit diminishing returns as fast as the
Shrek series did.