It is fairly obvious that designs from the computer straight to the printer is going to be the ideal way to produce plugs to make moulds from. If the printer is large enough to produce the various plug sections in complete units, then the symmetry and lines are going to be perfectly faithful to the mathematical specs coming from the software.

Kayak manufacturers are all ready CNC cutting plugs and molds with multi axis milling machines (subtractive).

http://www.fluidkayaks.com/us/research-development/
http://www.youtube.com/watch?v=l6LzSwf-Xvs
http://www.alibaba.com/product-detail/2014-hot-sale-rotational-CNC-casting_1592459023.html

The 3D printing technology (additive) in the OP video uniquely allows for creating enclosed hollow shapes; loose, linked parts within parts; and some printers allow for multiple different materials within the same printing, but it is long way from being practical for molds or plugs (it took 42 days to print the kayak) and doesn't offer any advantages over the subtractive machining currently used to make molds.

I would really love to have a 3D printer as well as a CNC router, but at this point I would choose the CNC router first because it is currently better suited for boat building. At this point the original post shows that a bunch of small parts can be pieced together to make a big thing, but I can see that some day the 3D printing technology could offer a way to make a one-off prototype of a boat like a kayak. A