alt Hacker NewsYou have conflicting requirements there - expressive type systems are not direct and simple. And elegant is subjective.
But seriously though: have you tried to see how far you can get with the design right now? You can start iterating on it already, even if the implementation will lag.
I do not have conflicting requirements. Expressive type system ARE direct and simple.
Expressive power is the ratio how strongly/clearly you can encode invariants to how complex and ceremonious the syntax of it needs to be.
See how JS, a language usually seen as a middling/mediocre language, can distill the basic good parts of OOP into very direct and clear idioms? I can just create an object literal and embed simple methods on them that receive the "this" pointer and use it. The constructor would be just a regular function. None of the cruft of standard OOP.
See how you define an enumerable union in TypeScript? Very simple. And yet I can think of many major languages that do not have this, certainly not with a lot of ceremony and complexity.
And I can go on.