They have now released the official video and, if you pause it @ 5:50, for example, you can read a list of some features included in the standard package and others in the subscription package:
I personally think that, if you like the Stark phone and if you can have a phone number for it, then you can stop paying for the plan on your phone and just use the Stark phone as your personal phone instead. The plan for my personal phone is more expensive than 13€/month and I have unlimited talk and texts and 50 GB of data.
Then the Varg app should allow notifications only in case of calls while riding so that you don't lose your GPS directions or generally your riding data just because your friend is calling you.
(For my needs my MX phone seems fine; maybe it's just a little too big and I haven't tested the battery consumption properly).
Another idea could be to have a dedicated MX version of the app. I wouldn't use the navigation but I'd like to have my laptime and telemetry data, provided the MX phone is suitable for that use: I don't know whether the GPS is accurate enough. Or if they want the power curves, the regen braking curves and the race mode to be paid, they could add the option to only pay for them and not for the rest, since especially people who do motocross probably like the curves and the race mode but don't need navigation.
Since over the air updates are included in the free plan, I guess that Stark Future can still connect to a Varg under free plan to check temperatures, malfunctions, etc. when needed.
Another idea that I have for the phone is that they could make it possible to record onboard videos while riding, for example by making new cradles that can be oriented.