Since the original series did not have a long-term plot, it's unclear just what they are going to show. Certainly, there's a manga for guidance. Recent record of anime extensions is far from stellar: Arashi and Haruka Nogizaka both were rather underwhelming even to stout fans. Almost makes one long for GONZO 2-parters. At least those unravelled in the final episodes and not right at the start of the 2nd season.
I quite liked K-ON, but I don't expect watching the sequel, unless it's a completely dead season otherwise.