Yeah I don't know about this S pen rumor for the S4. I think that's one of the selling points of the Note line, besides the larger size of course.
Personally I think the S4 will probably be just a jump up in specs (faster processer, better screen, more bells and whistles, more memory). Maybe a new design even?
But since nobody knows anything about the S4, the rumor mill will be working overtime the closer we get to the launch. Although it's fun to speculate on these things