Since Wilderness tasks and points are tracked separately anyway, it would be nice to be able to have an active Krystilia task at the same time as a normal slayer task. I think the commitment to "you have to do this task in the wilderness before proceeding with further Slayer training" discourages it more than it should.
And, for example, if you are assigned a Greater Demon task by both Krystilia and Duradel, the KC in the Wilderness should count for the Krystilia task first but not the Duradel task. I think this is better than just removing overlapping tasks from the roll pool to avoid task manipulation.