Polymaker ( http://www.polymaker.com/shop/polysupport/ ) just released a support material that does not have the downsides of PVA. It seems to be a kind of PLA that has very weak adhesion. Maybe its worth for the Ultimaker team to revisit Dual Extrusion with this material in mind?
Also, while a different Support material is definitely the biggest reason for dual extrusion, dual color is nice as well so I would really like to urge Ultimaker to investigate some more. I've bought two Ultimakers ( 1 & 2 ) and this is the only big thing that they are lacking. I must admit I also bought it expecting there to be dual extrusion in the future.
Cheers,
Mad