The halving changes the OTC landscape too. OTC buyers who previously bought from miners will be squeezed and will have to look elsewhere. Miners who previously dumped on exchanges, and there must have been a few, will find OTC buyers seeking them out. I expect far fewer mined coins will reach the open market from now on. There's no need.
Yet perhaps this is about creating a market of different Bitcoins in terms of their values based on their past. Perhaps the Grayscale realized that not all BTCs will be the same value in the future, and that some will not actually be usable anywhere else except on the black market. It is common knowledge that Virgin Bitcoins are sold at premium prices, which definitely suits the miners who have the exclusive right to them. I read an interesting qualification (speculation) about how Bitcoin could be classified into 4 categories by price, but also by how it can actually be used.
In the future, chain analysis companies and automated services would be able to classify coins (UTXOs) in several categories:
2% of all Bitcoins: black - located on, or several hops away from a known darknet/blacklisted address. These could be spent at black markets only. Exchanges and banks would immediately freeze these coins at deposit, and open an investigation with authorities.
40% of all Bitcoins: gray - coins of untraceable origin, assumed to be mixed. Extreme KYC/KCOYC/AML vetting will be required to trade or sell these coins in the "normal" world. Legally operating merchants in some countries would need to ID you before accepting payment.
55% of all Bitcoins: white - coins with a fully traceable origin, right from the moment they were mined or bought from a KYC/AML exchange. In the distant future, owning whitelisted coins would allow nation-states to practice "legal ownership" laws by forcing miners to accept only transactions signed by a trusted (central) bank. You'd be able to reverse an illegal tx, same way you can now reverse a Visa or PayPal transaction.
3% of all Bitcoins: virgin - coins with zero transactions. These would be used as collectibles or as monetary reserves in case Bitcoin replaces physical gold.
This may be just speculation, but it makes sense if we think logically, although the idea of reverse transactions is something that most today would not accept when it comes to Bitcoin. Obviously, it will no longer be just a question of investing in BTC, but also of verifying the origin of such coins.