If you can't get enough what I'd argue is Oblivion's best faction questline, Oblivion Remastered modders have got you covered. One of them's developed a whole radiant contract system for the Dark Brotherhood, adding 100 new targets you can slaughter over and over again if you really want to live Black Hand lifestyle to the fullest.
Wish Oblivion Remastered's Dark Brotherhood missions never ended? Well, this mod adds a huge new radiant contract system with, er, Morrowindy gacha mechanics
Source: VG247 (opens in a new tab)