I should really learn to code Java. Too many ideas, not enough execution ability.
Likewise, I should really learn how to mod with forge. I know Java fairly well, but modding requires a different skill set than writing something from scratch...
doesn't help that I tend to bite off more than I can chew. But hey, whatever.
An idea I had a while back but never really fleshed out - a mod that adds a "wonder building" mechanic. Essentially, you'd start out by building a large structure with a theme, and by activating some kind of core device within it, it would start influencing the area around it, terraforming it into a special biome with unique mobs and plants. So, for example, if you built a big, whimsical castle, you'd start getting Cheshire Cat mobs and Dr. Seuss trees. The larger the structure, the faster the terraforming would take place, and the farther it would terraform. It would give people a practical reason to make impressive buildings.
Another idea in the same vein, a mod that adds regional mobs to make the world seem more alive. I would like to walk through the world and see a family of beavers gnawing at trees by a riverside, and see deer flee into the forest as they detect a nearby player. The operative word here being regional - ideally the added mobs would only spawn within certain chunks within certain biomes, so you'd have to travel quite a bit to see all of them. This would make different areas of the same biome feel different, as you'd have different animals there. While Mo' Creatures and similar mods exist, I'm not looking to have a huge quantity of new mobs shoved in my face at once - instead, I'm suggesting a light sprinkling of interesting, rare ones around the world to discover at your own pace. Bonus points if the mobs work together to slowly reshape the natural landscape (i.e. beavers chop down trees and deer plant the saplings that drop).
I would also like a simple mod (either a BC addon or some generic storage blocks) that gave you more control over the order your pipes pull stuff out of inventories, and how many items they pull out.
Edit: Oh, another one. A Forestry addon that spawned some of the easier to breed Forestry trees in the overworld (non-fruit bearing for lag reasons). Partly to make the world more pretty, but also to cut down on tedium a bit.