New UI and content incompatible with older Roku boxes

Roku recently changed their user interface and added a lot of new PBS and PBS Kids content to their offering, but older models cannot run the new version of their software or display the PBS content.

I have two Roku boxes. One received the Roku Version 5 update, but the other is older hardware and is stuck with Version 3. (Was there a Version 4)?

I do not care all that much about not being able to use the new, improved interface, but I was surprised and disappointed that I could not see the new content. In retrospect, I can think of business and technical reasons for Roku not supporting the new content format.

Well, I am going to have to replace my older Roku, and, this time, I will be aware that it may not be capable of playing future Roku content. It would also be good if they published a list of their channels, indicating which ones are compatible with which hardware.