Two ideas for Poison and Disease. Nothing urgent, we've got plenty on our docket. This is something that came to me while looking at spell effects and I feel they would better round out how the maladies translate to something useful/dangerous in our gameworld.
Currently, neither are really threatening. They are always fortitude rolls and even if you fail, the actual effects can be removed by something like a potion of lesser restoration. As hazards for adventurers, they're hardly anything to worry about and as weapons to use in PvP and PvE they are a horrendous choice to anything that would force a fortitude roll(Death, Blindness, Ability/level drain). With both of my suggestions, while the actual effects are still removed by stuff like lesser restoration, the fact that you're still either poisoned or diseased begins to mean something for both you and your party.
Poison: While in the Poisoned condition, the subject takes 5% of their Max HP as damage every 6 seconds. This stops after the secondary roll(1 minute, 50% HP).
Disease: While in the Diseased condition, nearby allied creatures also roll against the disease each round. After 1 minute, this roll only happens once every hour(2 min).
I'm not sure about the implementation of either of these, if we'd have to modify each disease and poison script individually(unfeasible for all but the most popular ones), or if there's a general script we can modify for each condition. In any case, my reasoning follows.
Poison becomes an eminent threat, whether you can negate the ability damage or not. Trotting along after having been poisoned is a bit harder to do. It's also not solved by a heal potion, unless you want to wait until you got down to 50%, which is dangerous, or heal every other couple of rounds to negate it, which is costly in both time and resources. You've failed a fort roll, so by all rights, you should be suffering somehow, considering what else could have happened to you: death, petrification, or harm. For PvE, it's a usable tool to negate high regenerating creatures or simply to have some constant damage on a foe over time.
Disease becomes a threat to large crowds, both allied and enemy. For your party, traveling with an untreated sick person is serious risk. Even if they survive the first minute around you, every now and then you're going to cough, sneeze, vomit, or otherwise force your friends to come in contact with the disease. If you can't heal your ally, you're faced with the dilemma of keeping your distance and having them be rushed down by enemies alone, or weathering the sickness with them. For PvE, infecting one target opens the door to calamity among the ranks. Every round for a minute, the mob is saving against succumbing to the disease. The risk/reward of beating one opponent's fortitude roll pays off over time by enemies falling sick left and right and then infecting other enemies as well.
Edit: Math fix.
Edit Edit: Let's just all agree I can't math after midnight. I had it right the first time.