Edit:
It has come to my attention that many of cosmetic blocks that give no other purpose than personalize the crafts in question are not allowed.
(...)
While some may have a lower chance of being permited, I believe that most are reasonable enough to be added.

(It was omitted for some reason.)

sort of agree with part of this, but first of all ship-allowed blocks should be part of shipyards to have them save and repair ships correctly.
otherwise, a handful of those blocks would be nice to have allowed on ships, though a few won't function on ships properly and a few are functioning blocks on other ships and are purposely not allowed
specifically i'd agree with adding target blocks, flower pots, lecterns, looms, fletching tables, shroomlight and lodestones on ships. few of the other blocks will likely break off of ships and cause issues when interacted with/left to function and obsidian is a weapon for destroyers, and leaves are environment blocks that shouldn't be allowed on ships imo, plus can decay while moving if they're natural which would give piloted ships issues

I will give the blocks that I think should not be added and an explanation why...

-Leaves: They should not be added, because all land traveling vehicles (APCs, Tanks, Trucks, etc.) cruise/travel through leaf blocks. If they become part of vehicles, then when you release next to a tree, then you will merge to the tree (which is what happened earlier in the server, which prompted that change in the first place.

-Obsidian: I think Obsidian would not be a good block to add, because the goal is to be able to release land vehicles anywhere (that is not touched by players or is up against a tree). Obsidian generates above ground, and could merge to the craft. Also, if a piece of Obsidian does merge to the craft, then you would need a diamond pickaxe to mine it, or spend 5 minutes punch the darn thing.

-Shroomlight: So, we a person goes to light up their roads, there are not any light blocks that don't merge to any vehicle, except shroomlights. Shrromlights are the only light block that you can count on to light up your roads without getting merged to the craft.

The prime intention I had for leaves, for example, was it use on Wooden Crafts to give a more rustic way or the combo with Composer that allow to make some sort of a decorative "plant". Plus the Movecraft mecanism does not place upon moving the blocks that are part of the craft as naturally generated so the leaves would never decay, in theory.

In matters of blocks that own a secondary option by "right clicking", many other similar blocks are already allows such as chests, barrels, ender chests, furnaces, smoker and blast furnace (without being an alternative option to furnaces).

Obsidian (and the crying counterpart) were meant for mere decoration but, as I forgot their use as Depth Charges for Destroyers, it's best to leave them aside then.

While it's true what Speedy says, I see no fundament on your awnser. Just because it's the only current one that does not merge with any vehicle and can therefore be used as light source for roads and trails, it's your responsability to make sure said blocks to not merge.

Shroomlights are my favorite out of this list

Podzol, mycelium and moss blocks should also be able to be part of craft, maybe not podzol as it can be found on the world but more rarely, still i see no way adding mycelium blocks, nether nyilium, and moss blocks would be a problem, they just are good decorative blocks