As long as you only expect index as information on your iterator, that would work to some extent (basically the user can not override the selection model and expect it to work without complying to this interface, which I think is a ok constraint).

The iterator is async in this RFC, so the object can be whatever it needs to be.

I am not sure what you mean with the rest of your message tbh.

I am not sure how an iterator can be async, but I may be misunderstanding what you have in mind. As for index, I was thinking iterator<int> for the interface where the int is the index of a selected element.

Ah! With async iterator i mean just some random thing that is working like a iterator but async, like efl io model or smth. like that.
Well we can look what we are doing in the end, the index is just not what the multi_selectable is specifying, which is kind of a problem ... :/