It would seem if you plan an article forum with the review field you could only do it in a dedicated article node and you'd have to wait for XF to implement this for mixed, so I definitely agree. It is needed.
Self-placement would be best as it suits every need. You could edit a custom placement field into article threads and do so much more with them. Still upvoted as it's 1 step closer to getting to custom placement.
It would be nice if that "custom placement" was an option for custom thread fields. I believe that the below screenshot speaks volumes as to why we need custom placement. But, to those that it don't understand the above: It's not necessary have og:title as a visible item, before the message...
I can imagine if you use article threads for reviews, somebody writing a review may well want to add a star rating for the product they are reviewing, but in that case you would probably use a dedicated article forum, not a mixed thread type forum. And as thread fields are tied to specific forums then you would just tie the star rating to your review forums.
This is partly based on the fact I can't think of any reaons apart from a review that you would want a star rating. I'm happy to be told otherwise!
Yes please! I would like to add a 'Canonical URL' custom field to articles only. There doesn't even seem to be a class wrapper around this area saying what article type is selected so I can hide fields with CSS.