You can already enroll many/most EV cars in a VTG program with different utilities (we have National Grid in our section of MA). There is software on the back end but it worked with our 2015 BMW i3 so I would presume basic capability is already there. The restriction is principally with the utilities proving they can do revenue recovery / cost recovery by using these vehicles; restriction isn't Rivian, Ford, Volkswagen, etc. Many pilots with utilities underway in California, Vermont, New York, Massachusetts and elsewhere to prove out the economics--it seems likely this will prove economic value, and thus become formal programs, within 3-5 years (VTG, that is).
While in the near term we can all just enroll our individual EVs or other distributed energy generators (DEGs), longer term we will need something in the home to be able to manage the call and response with the utility. Potentially this could be your utility panel (see Span.io or Lumin Smart Panels). The huge list of potential distributed end items (smart hot water heaters, EV chargers, Tesla Powerwalls) it's better to enroll a single smart panel than 15 different endpoints, each of which undergoes firmware upgrades and separate login/password/etc. making it a fragile system. Bit outside this thread, but interesting to contemplate!