Almost zero AVRs (or processors) have USB Type B inputs. So, by and large, that will not work. A Roon Bridge product would be limited to S/PDIF or HDMI in order to connect to an AVR. That is one of the reasons why some are interested in using Roon via the network inputs present on almost all AVRs. But I agree that Roon currently is too niche, may always be too niche to attract the attention of mostly Japanese AV manufacturers.
AJ