Do you think it's not enforceable because of that definition? Revenue of $1M alone (not net revenue) should be a rough proxy of organization size. If a company makes that kind of money it should be able organize its expenses to pay a reasonable price for the software they rely on. There could be an exception for non-profits, if it would make more sense. If companies were rational they would already be paying the reasonable amount for "normal" open-source software, since unmaintained software in their supply chain also can also become a problem for them.
BTPL (I just think BTPL is neat) has these concrete terms:
>You may use the software for the benefit of your [small business] if it meets all these criteria:
* had fewer than 20 total individuals working as employees and independent contractors at all times during the last tax year
* earned less than $1,000,000 total revenue in the last tax year
* received less than $1,000,000 total debt, equity, and other investment in the last five tax years, counting investment in predecessor companies that reorganized into, merged with, or spun out your company