Just posted on the dot com announcement board.
https://community.ebay.com/t5/Announcements/Exciting-News-for-Auction-Sellers-Who-Offer-Combined-Shi...
Stay tuned, we’re enhancing this experience
We’re in the early stages of testing this solution, so you might start seeing buyer requests as combined shipping is gradually introduced. Don't worry if it's not visible to you yet!
Further improvements are coming to the experience, so stay tuned for future updates to be announced next year.
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From a quick read it doesn't appear to be applicable for BIN unfortunately. That would be extremely helpful considering majority of listings now are in that form and cause the most grief for sellers and buyers.
Note: This is still in the testing phase.
