Nice work on summing up the render farm landscape! Building on the information you presented, I'd like to make a few notes:
Blockchain-based solutions have a few challenges, both technical and operational. They usually rely on breaking frames into pieces, but not every frame can be rendered correctly this way. The nodes they use run on a variety of hardware and internet connections, which means the delivery speed can have ups and downs. And they are facing the challenge of licensing the 3D software, which means that at the moment they are either supporting only free software (Blender) or are tied to a specific vendor (as is Otoy's case)
Support is also a matter to consider. Cloud-based farms and public blockchain solutions offer a different kind of support to their customers than 'traditional' farms.
Getting started with using a farm doesn't have to be an elaborate process when it comes to preparing the project file. The processes are usually documented for each particular software. And farms can also offer one-click plugins to help with the packing and uploading.
In terms of infrastructure, there is now a new generation of hybrid solutions in the market. RenderStreet is one of the first render farms of this kind, combining both dedicated and cloud infrastructure for a better value for dollar and better availability. This translates into a more flexible service offering - from a unique low-cost monthly plan to a high-volume, cost-optimized plan dedicated to studios. There is also the benefit of a faster upgrade cycle for the hardware, all to the benefit of the artists and studios. And everything is packaged into an intuitive, automated interface.
(disclosure: I'm RenderStreet's CEO)