[Hemospectrum]

CLAP does not need to supplant all other plugin formats to succeed. Its real goal (arguably more ambitious) is to expand the set of features in the "least common denominator" of plugin formats. To do that, it only needs to win a race with one other format, which, as it happens, is officially already dead.

Plugin developers don't just pursue the largest revenue streams. They also try to take the lowest-effort paths to those markets. CLAP is carefully designed to be a low-effort path for porting old plugins to an SDK compatible with modern feature sets, which can then be automatically wrapped in comparable formats such as VST3. There are other such SDKs, such as JUCE, but they almost all require a much larger investment of effort to work with old codebases. The fact that CLAP also specifies a well-defined plugin format further enables developers to write automatic test suites, or adapt such test suites that were originally designed for other formats. In a certain subset of the market, CLAP has already been adopted for these reasons, and as far as its creators are concerned, it has therefore already accomplished its goals.

As you suggest, there is a certain possibility that Apple or Steinberg would somehow prohibit the use of third-party SDKs in plugin development, but in reality this would be an absurd thing to try. It would accomplish nothing, alienate the entire market, and promptly result in a flurry of lawsuits and perhaps even an antitrust investigation.