The rumour is from Taiwan as the headquarters of Sony. It is reported that Sony will release 12 inch Tablet that will be launched on the first quarterly of the next year. At least it should be on the next March, 2015.
This tablet will be the high-end one along with stylus. It seems that Sony very optimistic that it this product will be success on market. But there is no any leak at all related to the specification. Based on observers said, Sony Xperia Tablet Z2 (Sony tablet that was launched at Februari 2014) is the biggest mistake of Sony that created 10.1 inch tablet.
The source of this rumour is actually afraid to report about this matter since you can see that there are many vendors of mobile peripherals which have been involved into big tablet business, but, until now, they have not launched even one.
If the rumour is correct, then Sony seems will place its tablet with the rival, Samsung Galaxy Note Pro that also has 12,2inch along with stylus too. It might be hard options for you moreover if the tablets are launched simultaneously.