Have you tried the import expression as opposed to the import statement?
E.G. const foo = await import('foo.js');
E.G. const foo = await import('foo.js');
It looks like the reason it doesn't work here is because it relies on "this" being the window object. To make top-level await possible your code gets wrapped into a function, and in there "this" no longer points to the window. I am sure a workaround is possible, I'll make a ticket on github.