1;
Definitely new Raidbosses, or buffing some low level Raidbosses to 85 that are not being hunted anyway. Reward is not the main point here, it would just be nice to kill different bosses and not just the same ones over and over again.
2;
Stronger champion mobs, they could be all made to be really strong, just make them passive so they don't hunt solo players down.
3;
Maybe make an unused farming area level 85? With really strong mobs that need to be hunted in parties.
4;
Better Olympiad rewards, or some new form of PvP event?
Basically, all of these have one common thing, they are endgame content, from which the game could use more of, most MMO's do this well, but in Lineage 2 you just run out of stuff to do after a while.
As you said, these are just ideas, I'll try to come up with more! Also, I don't expect these to be implemented just because I wrote about them, but I think these are some good basic ideas to go by.
Regards,
Danielder