Software diagrams (such as class diagrams, sequence diagrams, state machines etc.) are a great way of conveying architecture at a highly abstract level, but they are a chore to create so we don't use them much. There are various easy-to-use diagram generators / editors but even then uploading images, sharing sources etc. is way too much effort.
mediawiki.org and Phabricator should make use of some software to generate diagrams straight from wikitext in an easy-to-create, easy-to-edit way so they get used a little more in our projects. Some candidates:
For Phabricator, this would have to be a Remarkup extension maintained by us (upstream has removed dot support due to security concerns and is not interested in other diagram languages - T9408, T12285).