According to the Japanese magazine Young Machine,   Yamaha will present a 650 c.c. twin user friendly version of the YZF-R series. This bike will compete with Honda CBR 500R and the Kawasaki ER 6-f (Ninja in US-Canada). 
The engine powering the bike could be the two cylinder cross plane one announced lately by Yamaha. A 400 c.c. variant could be produced for the requirements of the Japanese market. 


Comment: So far the YZF-R name was indented to uncompromised sporty bikes, in 125/600/1000 variants. Its rather peculiar if Yamaha chooses the same name for a conventional bike, given the extreme R6. Except if, the R6 will get the three cylinder engine announced by Yamaha, in an effort to compete with the Triumph Daytona, which could mean a new model name.  
Eventually, there has been considerable speculation already about the oncoming YZF R-250 for almost a year now, hopefully less scenarios will be leaked concerning this bike.