Joss Whedon announced at this year's San Diego Comic-con that the Avengers sequel will be the Age of Ultron.  http://www.themarysue.com/avengers-2-age-of-ultron/

So what does that mean for the end-credit teaser depicted in the first Avengers movie?  Will that villain feature in the upcoming Guardians of the Galaxy movie, which will include the Kree (who are at war with the Skrulls, which to me looked more like the guy shown in Avengers)?

I just hope that Whedon's telling of the Ultron story is better than the comic version, which seemed unfocused and anti-climatic.