I apologise if some of the below does in fact exist, I'd gladly find out!
There are three major parts of my workflow as project maintainer and contributor that I find lacking in Differential right now and are strong reason for me to discourage anyone from migrating to it. In addition, projects that have already migrated are essentially non-existent and blind to my workflow as a result. I've tried but even if I accept loss in productivity, I can't even find a workaround for these.
1. Casual notifications about new patches and merged commits (IRC notifications). - https://phabricator.wikimedia.org/T116330
2. Discover pending patches.
While Diffusion is a fine repo browser, it appears to lack any link back to Differential. Even when manually going to Differential, it doesn't appear to be any concept of "repo". It only has a global concept of "diff" and "reviewer" (e.g. you can list diffs for review, and your own open diffs). Unlike Maniphest (which has a concept of projects that have their own pages with useful outgoing links). There is no list of projects with a link to see a project's patches. This unlike Gerrit or GitHub where projects are linked to searches for open patches or open pull-requests. This makes it very non-transparent for potential consumers of our code, and casual contributors to find out about open patches. This is an important indicator for developers to determine the health of a project. It's also an easy way-in to for new reviewers, and an important interface for project maintainers to easily list open patches from time to time. Without this, I expect our code review habits to become even worse than they already are.
https://phabricator.wikimedia.org/differential/ (no projects listed) -> https://phabricator.wikimedia.org/differential/query/all/ (no repos named alongside the diffs) -> https://phabricator.wikimedia.org/D229 (links to diffusion) -> https://phabricator.wikimedia.org/diffusion/GOJR/ (no link to query to differential).
If I see this correctly, there is simply no way to naturally get to a list of open patches of a project.
3. Notification about new patches and merged commits.
There is appears to be no way to subscribe to a repo (e.g. as a maintainer of that repo) so that I may be notified of new diffs and/or landed commits. This is worse due to #2, which would've been a workaround (albeit a costly one, due to pull:N vs push:1).
In addition to these workflow concerns, there is also Continuous integration of course. But that's a separate issue.
I'm bringing up these concerns now because contrary to what I expected, Differential is being adopted by quite a few repos now despite it being premature.
-- Krinkle