The problem is, Minecraft cannot comprehend moving blocks like the chests in the boat unless they are temporarily turned into FallingSand entity. I advise Mojang to make the chests chest-in-minecarts.
But good idea.
I also think that the new things (eg hammer, plating) in this should be used for things other than boats.
And I think this would be a good addition for Minecraft 2.0 (or 1.0 while this version becomes Gamma).