John said, "don’t make apps that might get rejected. or do a proof of concept first and see if it will be admitted."

Unfortunately, it's not that simple. Just because one app has been approved does not set a precedent for future approval with Apple. There are many instances where app X gets approved with a set of features and app Y gets rejected for the same features.

There is no absolute consistency in the review process on which you can reliably depend.

Also, there are many documented cases of an app being approved, several more updates being approved over the course of a year and then a newer update being rejected when no significant features have changed. (As a developer, I've also experienced this personally in the review process, and it is this inconsistency which is the most frustrating part of the approval process.)