That's great news that you know Mark! We have talked extensively with Mark about the design of Pony, and he agrees that it is indeed a capabilities type system, and that it is capabilities secure.
Hmm well if Mark Miller says Pony is capability-based then it must be. I apologize if I've misunderstood. I'm confused, though, by two things:
1. Your documentation introducing capabilities specifically says: "Pony capabilities are completely new, no other language has them." If you really mean "capability" in Mark Miller's sense of the word, then this statement is incorrect. Many object-capability languages exist.
2. What your documentation describes as "capabilities" looks to me like type qualifiers. The documentation says "A capability is a form of type qualifier and provides a lot more guarantees than const does!" But this doesn't sound anything like capabilities.
Is it possible that Pony is an object-capability language but you are also using the word to refer to a different concept? If Pony is actually an object-cap language then that's excellent, and I even more so encourage you to rename the type qualifier concept to avoid the confusion!
FWIW, Sandstorm is very interested in adopting a high-performance ocap language, but would probably shy away from one which uses the word "capbaility" to mean something else, for fear of confusing developers.