I know MC lets you import guide data from various sources but a really cool feature for WMC that has been long gone for some time was web content in the TV guide. I think this would be a useful feature that would grow on users and help JRiver compete with the likes of Kodi, etc. provided the feature is baked into the core program and doesn't require any 3rd party software (In the case of Kodi, Pseudo TV).
Thinking about what is possible should this become a reality, I will try to illustrate how I might implement this feature in my own home. I use two separate paid programs to create DLNA content on my home network so that any device can play said content (Free options are out there as well) and I have found old WMC plugins that can easily read content from said sources, and play them fullscreen without issue. This implementation still isn't the best solution, and it doesn't break down my web content into a user friendly "lead me by the nose" format BUT adding these sources to the TV guide would go a long way in doing so. I know this will never happen with WMC, and with programs like Koid, this task becomes burdensome because I have to learn how SEVERAL pieces of software work, and maintain them.
From my limited knowledge, I think JRiver implementing a feature where it can display data from a DLNA source, and launch said content seems like it would go a long way in giving it an advantage over its competitors. I believe that if JRiver were to implement this feature, it could do so in more "integrated" way from a UI standpoint, it would be more stable, and the company could easily claim that it has SURPASSED its competitors in terms of exciting, flashy new features. I think you could probably win over quite a few frustrated Kodi/Pseudo TV users. This would also allow you claim support for streaming services such as netflix, amazon, etc. via whatever third party programs the user chooses to implement. At the very least it would give users access to basic web content, such as news, podcast, sports, etc. in a user friendly interface that integrates tightly into the way JRiver already looks and feels.