Im not necessarily saying pick him but he is a specialist 3 which we don't have. We played Peter Ingram their against the Bangys, im reasonably confident Williamson would go as well there as Ingram will.
Can't see him getting much of a go in the ODIs this year with the World Cup next year, Ryder, Guptill, McCullum and Ingram have the openers and 3 spot locked up. Maybe take him to the T20 world cup but that isn't really his game so wouldn't do him much good anyway.
The way people talk about him and the runs he is scoring isn't dissimilar to what Taylor was doing at a similar age and part of me thinks it is almost a waste not utilising the talent that is out there.