In my opinion, more of an 'airship/boat' mod, essentially the same kind as
this one here, would add a lot of creative depth to the game. The first major hurdle would be getting the damned thing working with 1.4.2, perhaps contact the developer of this or mods like it to try and get them on board? What I like most about this mod in particular is that it isn't just airships, you can make boats too. You could really expand it to be it's own major modification. For instance, integrating it with BuildCraft landmarks to set the ship size? That would save you from having to mess around in config files to get certain blocks to move with the ship, though you would have to be careful not to get stray blocks mixed in. One problem I see would, in the mods current state, it is overpowered as
all get out. So add in some complexity, here are some of my thoughts:
-Add components like propellers, engines, balloons, to give a ship or boat lift. Give blocks a certain weight. Your lift must exceed the weight to even get off the ground, and you'll go very slowly unless you've got a
massive lift-to-weight ratio. This will, hopfully, keep rail networks a viable option.
-Fuel consumption. The more components/lift it needs, the more fuel it takes, though if it runs out it should simply stop in place instead of plummeting to it's demise. Same if components that add lift are taken off and the weight once again exceeds it. Maybe special furnances? Link it to IC2's EU system? Nuclear powered airships? Yes please!
-Make the actual components to craft an airship fairly expensive, or have it in tiers/combine. A basic piloting block might power an airship no larger than 10-50 blocks, a larger airship might need 3, or 4, or a higher tier. Airships should be a reward for sticking to your world so long, or a goal to work towards.
-Boats should be cheaper then airships, and could be a fun way for players to cross an ocean in style.
Airships would add a great deal of creative flexibility. Airships or boats players can make, a nomadic player who simply explores. I think that there is a very good case to be made for including such a mod, should it be working and balanced. Which I understand is a daunting task, but should be considered if and when the chance presents itself, or at least attempt to contact the old developer(s) to see if they'd like to come aboard (my future airship).