This would provide ability to set certain products to be only purchasable using the allowed payment methods. For example, this would exclude product from global payment methods to be purchasable only by credit card.
Most will let you use product attributes to trigger when payment methods are available/restricted at checkout.
I understand that you're looking for a native feature to accomplish this, which I agree, would be nice. However, with so many reasonably priced extensions that accomplish this, it may not be a high priority to add this to Magento's core. There has also been a lot of focus on trimming down Magento's core to make maintenance, upgrades, patches, and other work easier, helping to manage the total cost of ownership of a Magento site.