Consider making window focus mouseup instead of mousedown

Watched a former apple and google asset talk about user interface issues at the Ubuntu Summit:

https://www.youtube.com/watch?v=1fZTOjd_bOQ

He points out a usability issue most GNU/Linux desktops (except KDE) have: if you try to drag and drop from a window behind the window in focus into an active window then you get a problem since GNU/Linux window managers change focus when you "pick up" an item you'd like to drag into the window the (previously) active window.

I can honestly say that I've never thought about this or considered it to be a usability problem myself. However, I immediately understood why focusing windows on mouseup instead of mousedown so drag and drop is easier on small screens would be preferable.

I tested how this works on xfce4/xfwm just to see how that behaves and I find the behavior the Ubuntu asset is complaining about.

I think this is a Enhancement/Feature Request worth considering.

I don't think this would have any negative impact. If I click on a window in order to get focus then I don't think it makes a practical difference if it gets focus on mousedown or mouseup. However, as I said, I haven't previously thought about this or studies this problem and I am not a user interface scientist so I don't know if there's reasons for current behavior I'm not considering or if there's any negative impact for current xfce users.