What problem do you see this feature as solving? Can you give specifics?

https://secure.phabricator.com/book/phabcontrib/article/feature_requests/#describe-problems

We expect sprints and milestones to come from Subprojects. So if that is your main problem, we'll just merge this task there. See T3670.

The point is to give a more powerful visualization to Phabricator Kanban.

This will help to better manage boards with many cards (with possibly filtering row-columns) but more to have even different viewpoints on the same task.

If you follow link provided you can find more examples and arguments for the purpose. Around the same link there are even more pages as:

• Description of different viewpoints ("multiban"): http://www.targetprocess.com/blog/2014/01/stuck-with-kanban-consider-multiban.html
• Example of use: http://www.targetprocess.com/3/portal/use-cases.html

We don't build features / solutions for the sake of building them, we need feature requests to state the problem they have with using Phabricator and only the problem. We may choose a different solution to solve your problem, one that solves many problems other real Phabricator users are encountering. If you can't state a problem you are having, it's not clear to me what we're building and why.

Filtering workboards is achieved via the filters at the top of the board. Sprints and Milestones will be better achieved with subproject support. The main issue is any problem you are currently having with workboards is likely already filed and planned under other tasks, so this task as currently stated, is not something we'd pursue.

This feature will for example solve the problem of visualizing all-together the tasks coming from different subprojects, without having to visualize the sub-tasks in each sub-project or alternatively having to have all of them mixed up in one (single dimension) Kanban.

Having them visualized in this way you have also the possibility with drag-and-drop of changing not one (as now) but two different "variables" in one time.

Missed in the first instance this nice video: http://www.targetprocess.com/kanban/

(it is not about solving problems, it is also about enabling possibilities: http://www.targetprocess.com/solutions/scrum-for-a-company/, by processes and roles)