Can you make a convincing argument that copyright ought to be transferable in the first place? I'm not certain it shouldn't, but this thread has made me realize I've never heard a good reason for it.
Liquidity for creators, without which some wouldn't have the time and money needed to create and publicise their creation. Its analogous to being allowed to sell [in part or whole] the ownership of your startup before accruing any profit.
Still, those who provide liquidity for creators should not be able to profit from a work any longer than the original creator would have, given the same resources. In other words, copyright should expire after the same fixed amount of time, whether it's owned by a person, an estate, or a corporation.
How does restricting transfer of copyright affect this? Is it that hard to get around? An artist wouldn't be able to completely sell the 'rights' to his work but he could certainly work out an arrangement whereby some record label or studio or publisher, etc., agrees to distribute his work for him in exchange for a portion of the proceeds. The only difference is that after the deed is done, the artist still owns the work and can work out a similar arrangement with someone else, should he choose.
This isn't uncommon even now, actually, but especially with yet-unknown artists publishers will often push pretty hard against it, and usually get what they want. I think removing it as a possibility would be good for artists in most cases.