Timeline would increase it's usefulness if you were able to choose a main Grouping and then a sub-grouping for the tasks.

I have my timeline grouped by a custom field, thats great - but now I want to organise the tasks that are showing in each of these lanes by their assignee.

So the timeline would look like:

Custom field 1

- Assignee A

- Assignee B

Custom field 2

- Assignee A

- Assignee C

I am using Assignee as an example, but I'm sure that any combination of all tasks fields would be useful to be able to combine.