Crosscut

I think it's important to consider the defaults we are setting, and what those defaults are going to mean for how the language will be used. (I alluded to that before.) And I think I want Crosscut to be a language that allows you to build airtight abstractions where that makes sense, but that doesn't push you into doing that.

Having nominal and opaque as separate concepts might be the best option in that regard. Each would be available to you, as a tool in your toolbox, but they wouldn't impose on you. You wouldn't feel forced to make every API restrictive from the start, doing more harm than good.

The natural way of doing things would be all structural, all public. Which might lead to a rather relaxed style of building APIs, where everything goes. But where it makes sense, you can reach for specialized tools to tie things down. Who knows if this is how it'll actually be; but I like the thought.