Except when that business is in making plugins for popular software. At least, many people seem to base their businesses on making plugins. In fact, even making

Except when that business is in making plugins for popular software. At least, many people seem to base their businesses on making plugins. In fact, even making apps for a particular platform or operating system has this problem. The real question to ask is the likelihood of that foundation being lost on short notice. In this case, since the User Terms forbids building upon the platform, to do so would clearly be a bad idea without getting specific permission (possibly by offering a commission).