All we know about a potential specification is that rumours give this 6GB of GDDR6 memory with a 192-bit bus. This would place it conveniently right in the middle between the 8GB of the RX 5700 at 256-bit and the 4GB of the RX 5500 at 128-bit. If the rest of the specification fits that pattern then it should be a decent card at a reasonable price. That's not the most exciting pitch in the world but this is ever the curse of the mid-range product.
There is no word on price as yet, nor any word on the specifics of availability. The Navi cards so far have either released in a limited fashion to the OEM market as the RX 5500 or held off on custom coolers for a while as with the RX 5700. So a January release for the RX 5600 could mean a brand new range of graphics cards on the shelves, or it might mean you can only get one in a pre-built system, or it might only be available with some sort of standard cooling. We won’t know until it happens, and it might not be happening, we’ll have to see.