There's been a lot of proposed replacements going back to the 1980s, some of them even perfectly working prototypes or limited service rifles (spetsnaz etc.) - just that one hasn't ever been adopted into service. Most of them are modernized derivatives of the AK anyway so I don't think there's much to worry about.
Personally I'm a fan of the Abakan:
http://en.wikipedia.org/wiki/AN-94 I hope something like that gets adopted.
The downside, though, is that it is a somewhat more complex and sensitive rifle than Kalashnikov, requiring better care and training. Still, for a proper and professional army service, that shouldn't be an issue.