i don't have any idea how easy or hard it would be, but it would be really cool if there was a plugin that allowed people to build even higher than they already can. if there is a plugin that already allows this please let me know
This is not what bukkit is for. Bukkit is for stuff like anti grief, expanding minecarts, not changing core mechanics that need a client mod to work.
The client can only handle 128 blocks of height. What a plugin could do is change sea-level. You could set it to position 32. This would mean you can only dig down 32 blocks, but would give you 96 blocks above sea level. However, even that would be pretty hard. There is a CHUNK_GENERATION event (planned). You would have to run the plugin all the time. When a new chunk is generated, it could delete every 2nd row. This would compress the land vertically, while still allowing deep ores to exist. However, I think chunk generation is a 2 pass process. "Far" chunks are generated with just stone/dirt/air. When you get near, the algorithm adds ores etc.
I know changing max hight is not really practical at this point but what an idea. Sky Towers 1000's of blocks hight and even sky towns. I can only imagine.
