Article was updated and now says it'll launch with those services.
"TiVo Plus will include video on demand services from Netflix, Hulu, Amazon Prime, YouTube, content provider Xumo, entertainment company Jukin Media and newspaper publisher Gannett. More will be announced in October. Shull said TiVo is still in talks to add other services, such as NBC, SlingTV and TikTok."
So... I guess Plus is also limited by the apps available for its given platform. Apps like NBC, SlingTV, Tiktok (barf) are more likely to be available on the dongle than the DVRs.
List of Xumo channels for smart TVs:
XUMO » Channel Lineup for XUMO on Smart TVs & Roku