Nice. I’ve actually been tempted to try and tinker with this myself but so far a lack of time and a lack of relevance to my projects has forced me resist. But we’ll see. I’ll post if I do and can come up with any improvements.
I think that the best possible result would have to use ray casting to project the billboarded quad onto a vertical facing quad and find the depth value that way. Then each pixel will be have the exact depth that it “ought” to have. For my purposes this is overkill, however others might still be interested is something like this.