It’s relatively new and in my short discussion with OTC Markets it simply requires a MM to request it for a grey stock in which they have unsolicited orders.
It’s only been in operation for about a month, and from what I can tell it really hasn’t changed anything. Some have speculated it was done to allow holders who work directly with broker/dealers (insiders and such) to increase liquidity so they can sell.
One grey stock I have watch went down when it was made “Expert Market” so that would suggest there might be something to that speculation.
Regardless there is no public quotation, and it wouldn’t change a thing WRT the OIP for revocation.