> For a mechanic who is looking for the amount of torque needed on a bolt this could be perfectly viable, for example.
We're going to start talking past each other pretty quickly if you think this is worthy of a (software) service subscription. Torque specs belong in a manual (ideally on corporate intra-net or paper); I'm talking about when the engine is deeply unhappy, and you need more to go on than a driver reporting a yellow check light.
In the case of the latter, I'd say it absolutely deserves to be a 20 year old program (which tend to be lighter) that runs entirely offline. The last thing any garage wants to do is chase hardware requirements or search for a wifi signal either out in the yard, or in between hoists, lifts, and miscelleaneous heavy equipment / tooling - all of which tend to trash a wifi signal.