There are a few threads mentioning this but they are all very old and seem to not move forward… The timeline view should offer the same filtering and sorting options as the list view. For example, I have a project for each Team member to manage their workload (better than the portfolio so far). So a team member would have a bunch of tasks all belonging to many different projects. I created a custom field named Project Label that helps me identify easily which project the task belongs to. (Not using the Projects field because those tasks are visible in many projects responding to different needs in the organization)
→ I can organize my List view with this custom field and it looks pretty good, all sections taking the name of that Project Label. Very easy to see all the tasks a team member is doing per project.
→ Now if I want to see how much time it takes for that person to work on that project, I would go to the timeline but I can’t filter per project and I don’t see why it’s not already available because it doesn’t seem to require any new development really…
I’m gutted to discover that Asana doesn’t support it’s own filter options in the timeline view… I had huge ambitions for utilizing the timeline view, but this completely prevents them.
Once again, off to another tool I go… 
I feel you… I had the same excitement until I really try to use it and find it too buggy. The lack of filter prevents from actually getting information you really need. The layout is hard to read, no lines no grid, no options to remove weekends, no option to a a lag time between dependent tasks. The list itself doesn’t even adjust the dates when they are dependencies … what’s the logic behind? Asana in all it’s different views and features has always something missing or even just not working. Asana is an unfinished product and has had enquirers from the communities for 4 years related to timelines and they still didn’t change anything. Focus on the real things Asana please. Who cares about putting a like on a task
We also need to be able to filter the timeline by custom fields. This week we were planning humanitarian projects for the next fiscal year. I have a project that lists each potential project as a task and each is assigned a project type. We needed to be able to see each project type in the timeline view separately. The only way I could do this is to “complete” the tasks of a single type and show completed tasks on the timeline. Very cumbersome. Also, I don’t see in the list view a way to filter by more than one project type (the project type custom field is a single select). I should be able to filter more than one item from the same custom field, e.g. New Wells and Well Repairs together.