I think this feature may be retired, or at least hidden until eBay sort out the new Q&A feature, and the option to display Q&A just hasn't been removed from the message system.
A while back, eBay introduced a different option where members could submit questions about items directly from the listing, however the question was actually emailed to other sellers of the item, as well as anyone who bought it previously, and sometimes the seller of the actual item did not receive the question - it was just meant to be a publically posted question, that anyone who sells or purchased the item could answer.
But it caused a lot of issues - questions meant specifically for that one seller were posted (eg combined postage Q's), and due to the email notifications that came through (which didn't explain what was happening well enough), a lot of people assumed the questions were scams or just spam, so that seems to have been put on ice for the time being, too
The introduction of the feature, though, would suggest eBay are primarily thinking about items that are perpetually available in the same condition (i.e. new), from multiple sellers, rather than other scenarios where the feature was handy.
