The Skylanders model isn't really designed with longevity as its main concern.
I would argue that it does have all the markings of a long running franchise. It's all in how you run it. I'm mixed on Activision's report card to date. 30% decline in one year is a huge concern to me---will the decline continue or will they move back up? Stay tuned. I'd argue this Nintendo exclusivity may artificially bump the numbers relative to the real families playing this game. It's a bit of shell game this time.