But there already is a bright line rule here, it has just not been diligently enforced up to now. The basic argument is that the Amphetamine app has been able to slide for so long that the ToS provision it violates should be treated as a dead letter, or as if some statute of limitations had expired; the Amphetamine brand has existed so long (and under such favorable conditions) in the app store that the developer now has an economic interest in the brand, gained through a reliance on Apple's non-enforcement of this ToS provision.
The developer could try suing Apple on the basis of laches, the legal doctrine whereby if one party has 'slept on their rights' so long that the situation changed, they can't suddenly decide to enforce a term later. But there's no hard and fast rule about this, and since it would tie Apple's hands they'd probably fight it tooth and nail, throwing enough legal resources at it to wear out any opposition.
Apple has accused Amphetamine of violating the following guideline:
1.4.3 Apps that encourage consumption of tobacco and vape products, illegal drugs, or excessive amounts of alcohol are not permitted on the App Store. Apps that encourage minors to consume any of these substances will be rejected. Facilitating the sale of marijuana, tobacco, or controlled substances (except for licensed pharmacies) isn’t allowed."
The developer could try suing Apple on the basis of laches, the legal doctrine whereby if one party has 'slept on their rights' so long that the situation changed, they can't suddenly decide to enforce a term later. But there's no hard and fast rule about this, and since it would tie Apple's hands they'd probably fight it tooth and nail, throwing enough legal resources at it to wear out any opposition.