Dangit, when are WE going to get a new rifle? Something with a piston that doesn't take 6 hours to clean, doesn't hate lefties, and require three hands to operate the charging handle maybe?
That said, there should be no hurry. Honestly, though, there's not a rifle out there that's truly good enough to justify the cost of replacement of the M4/M16, but that's a topic for another day.
BTW, if your AR takes 6 hours to clean and 3 hards to charge, you are doing something wrong. Also, there are few infantry rifles that at more lefty-friendly than the AR system, with it's ambi charging handle, brass deflector, etc. The Beretta ARX-160 for sure, but not many others.