That a custom field has been updated, or where a task originated from, etc. can reduce productivity, so a possibility to toggle between "real" comments and all activity - just like in Trello - would be great.
Ideally customizable in Settings what belongs to which of the 2 groups:
Ex.: Custom fields A, B and C - to be considered as "real" comments, whereas all other custom field activity can be hidden/displayed only when selecting "all activity".
What about multiple groups. Ex.
1) strictly user typed comments only
2) cf. 1 + custom fields A, B & C
3) all activity
Add read/unread and/or marked as important comments filter to either group.
Comments/discussion welcome.