I know Timeline has the incomplete/completed task filters, but it needs more filtering. Moreover, the filtering system should really be the same (I think) for List, Boards, Timeline, and Calendar views, and it should be more advanced than what is offered for Lists right now.
For example, I may want to filter by 2, 3, or whatever number of custom fields. I should be able to do that. If I wanted to filter to a specific assignee, by a specific date range, and by 3 other custom fields, I should be able to do that.
One example of how we would use this is to make an editorial calendar. We have multiple teams at times, working on the same campaigns, and other times working on one-off projects. Upper management wants to be able to see these projects, but not really on the project level, they want to see what’s being delivered… but not down to the task level. They are tasks, but they are more deliverable tasks than just straight up tasks. But if we put all these deliverable tasks on this editorial calendar, it would be too much to look at all the time. But having a way to drill down and see just stuff form one team, or just projects that fall under this or that custom field, would help filter things out so it’s more reasonable to look at. That’s just one use, I have multiple possible uses for advanced filtering.