I looked through most of them. I am very critical of proposals to games, because they affect everyone who play the game unlike mods which are user side. Here is the criteria I use for a good idea proposal.

1. It cannot be arbitrary, the addition needs to add depth, not add width. Beetroot is a prime example of a arbitrary addition, it does absolutely nothing but serve as a red alternative to the carrot.
2. It cannot be theme breaking. Minecraft is a medieval based sandbox game. A change that would make Minecraft less sandboxy, or less medieval. is theme breaking, hence cell phones and campaigns should not be added to minecraft (yes these are both suggestions Ive seen in this contest).
3. It cannot be overcomplicated. I cant compell myself to use mods like Witchery or Tekkit because they are unintuitive, you need a guide to do anything at all. The only exception is command related things because more options means more freedom, and you arent required to write complex commands in order to play Minecraft survival to its fullest.
4. It cannot be unbalanced. A game is defined by its balance of its challenge. Ideas that make Minecraft too easy often make the game more boring. Ideas that make Minecraft too hard often make the game frustrating.

I like this idea because.
1. These Boats have a purpose, cannon ships would be used for water combat, sail boats would move faster, fishing boats would increase effeciency of fishing by letting you have two active rods. They have unique uses, so it isnt arbitrary because currently Minecraft has no better alternative for water combat or fast water travel.
2. These Boats fit well with the theme. It also compliments the sanbox genre by openning up the world even more.
3. Its very simple in concept, all though I think the crafting recipes could be tweaked to make a bit more sense and be more intuitive.
4. Having a boat with explosive cannons does not break the game, because boats are limited to the water, it doesnt make it easier to explore caves. It only makes it a bit easier to explore the ocean, and this is balanced by the fact that these new boats require a bit more material than the regular boat.

Here are my suggested expansions on this boat idea: Obsidian boat that survives in lava. Chest (storage) boat for moving your gear across seas. Kayak for better turn control and better ability to swin against currents.