And further, I'd love to be able to export a history of tasks. Particularly, my stakeholders have a habit of "oh, just one more thing..." after the task has been closed, so i'd love to be able to track the 're-open' rates of projects and tasks.

or be able to delete erroneous/unimportant activities from the history would be great

From support ticket: I'd like to track the history of comment edits/ deletes

I wonder if this feature would support scenario of searching for tasks that have status "Rejected" before "Close"

not sure if this has been mentioned elsewhere. if the above is planned, then it would be useful if changes to custom fields was also captured in the task history, and if the task history filter could be applied to these.

use case: A special field is created for tracking something (e.g. cost to date, design brief change from client, etc). then, at the click of a button a breakdown could be displayed (e.g. a list of all the changes a client made, with dates in a simple list). Clicking on any of these could take the user back to the original full task activity feed.