As recently as a month ago, @Emily_Roman posted that a similar request is not under consideration at this time, so I suspect that this isn’t happening in the foreseeable future. However, the use of bookmarklets has been mentioned in other posts as a workaround for expanding all subtasks at once, and I have found it to be useful at times. It doesn’t do what we’re asking for in this thread, but it’s better than clicking on every task with subs in it. This only works when using the web interface, FYI.