I feel that the most important part of this is having clear data ownership rules to assure users that they actually own their data. That is, they can take it in a machine-readable format whenever they wish, and with it remove the right of the company to continue holding the data. I am very much in favour of stepping up personal analytics, but there's no way I'm going to just hand over some of my most personal data and hope that the company doesn't use it as the ultimate lock-in tool.
If a web platform is developed to provide storage and an API, the only way I would trust it is if it were completely open source and users were encouraged to run their own nodes (as well as supporting easy data migration between nodes).
Considering your early adopter audience is probably going to be highly technical, I think this matters. Having a clear benefit also makes the privacy cost more appetizing.
But frankly, requiring users to run their own nodes is a terrible idea and would doom a startup that followed this advice to failure. It would please some early adopters, but make growth essentially impossible.
I don't think it is necessary to require users to run their own nodes, but simply allow the option and encourage a community to form around doing so.
Basically, set up a scenario where the startup is service-oriented and must stay honest because it competes with its own community for users on the official node. Most users will prefer to trust the startup with their data for ease of use, and there will be an enormous amount of credibility gained by having a mechanism to keep the startup's greed in check.
I didn't mention this, but the value and the revenue will come from solving people's problems. I think things are really well aligned here. You have a really cynical view that most people don't share. You're probably closer to reality, but what users actually care about matters more than reality.
I should probably mention that I have put quite a bit of work into developing a similar system myself. I even prototyped and pitched it a couple years ago, but basically got shut down by judges who were offended by the kinds of data I suggested tracking (i.e., everything).
I am quite cynical about companies that extract revenue from personal data (LinkedIn, Facebook, Google, etc.), and I recognize that most people probably aren't. I suppose I am more of an idealist and would have trouble sleeping if I inadvertently created Big Brother, which is why I would risk hamstringing such a startup to try to ensure that it stays honest.
If a web platform is developed to provide storage and an API, the only way I would trust it is if it were completely open source and users were encouraged to run their own nodes (as well as supporting easy data migration between nodes).