Missing the point...
The issue here is not just that Docker is looking for how to pay for its existence. It's also about how reliable of a supplier it is to companies that rely on it. While having tiered pricing is great for a company going in, being faced with changing rules as time goes on can be highly destructive to trust. Just ask anyone who has done business with Oracle or Microsoft.
So while creating new paid tier requirements may be the only way forward for Docker, and while the initial requirements are quite reasonable, the concern for businesses is what future changes might happen. It's sort of like the income tax that was introduced just a bit over 100 years ago at 1% (going to 7% for those who made more than 13 million in inflation adjusted dollars). But those numbers hit 23% and 94% just a few decades later.
So what's Docker's next move? Tighten the screws some more? How?