I've attached D14359 which is running in our local phab instance and mostly works. While the rule works as intended, the status doesn't want to display properly. I don't expect anyone to accept this as-is, but I thought I'd share as a starting point for anyone who has the time and knowledge to do it The Right Way.

When creating the rule, the entry box for status is rendered correctly, and auto-completes as expected. But when you save the rule, the status was being displayed as 'Unknown object (???)'. I modified the patch to display the key value instead, which at least lets you know what's configured.

And then when you re-edit the rule, the entry box now shows the status value as "Unknown" (looking at the source, it has the expected key but isn't being mapped correctly). If you delete the current value (or just add another one, see below) the status fields are mapped and rendered correctly.

The other issue, which seemed lower priority, is that it allows multiple statuses to be entered. I couldn't find an obvious way to limit it to a single status (and comments in ManiphestTaskAssignOtherHeraldAction.php make it seem like this is a known issue), but applyEffect() is only using the first status.

I'm also happy to fix up this patch myself, if anyone can give me some hints as to what I did wrong :)

Oh, I should have read that comment more carefully. You tested more thoroughly than I did.

I'll see if I can fix the "Unknown Object" issue, it's not trivial and my comments on the revision don't address it.

I think it wasn't that bad thanks to a similar set of changes elsewhere from D14669, which I wrote yesterday.

The "only one token" thing is a known issue; it only affected one rule (I think?) before these two recent ones and I don't think it's a major usability issue (users are unlikely to enter multiple statuses, and I can't come up with a reasonable behavior users might expect entering multiple statuses or priorities to have) so I haven't bothered fixing it.