Judging from the small example in the readme, the language looks pleasing to the eye.

What’s under the hood though? What are some of the technical choices, performance characteristics and longer term goals?

The current implementation looks like a compiler to a stack-based bytecode with a straightforward textbook interpreter. For example, here is the interpretation of the Add bytecode: https://github.com/egranata/aria/blob/master/vm-lib/src/vm.r...

So to a very rough first approximation, performance characteristics should be in CPython's ballpark.