So, I've decided that once the API is released for modding Minecraft, I'm going to try my hand at it. I've got this idea for a custom mod to run on a server, that I think can be fun. Really it would kind of be a mixture of existing mods with a twist. My ideas are as follows:
1. Ultra-Hardcore: Like the ultra-hardcore mod, where health is only regained through golden apples and potions. Maybe setup so that it doesn't require as much gold (the normal recipes, not the modified ones).
2. Hardcore: Once a person dies they are respawned either in a special area or are respawned in a mode where they cannot affect the world.
3. Mo Creatures: Basically more mobs, more hostile mobs, maybe some new friendly mobs that will help you? Possibly a way to tame some of the hostile mobs.
4. Worldgen: Create a custom world generator that will randomly add a few traps to the world, and generate a world specific for this (creating the border around your map), allows random spawns for each player (instead of a central spawn point shared by all).
5. PVP Bonus: When you kill someone they have a chance to drop items on death. This will be configurable, or possibly based on something specific (length of survival = Better loot).
6. Scoring: possibly a system to score a player. Base it on a number of things, like blocks collected, damage dealt (pvp and pve) player kills, damage healed, etc.
These are just some general ideas, I'm not really familiar with modding for minecraft, but I once there is an API, I'll give it my best shot. I know some of these things I can accomplish using existing mods, and I might use them, depending on the work involved in creating my own mod.