Completion? The other selectors all have 'em. This should be carried over into T117736 but it stands out here as is. It'd be nice for anything wanting to access it to avoid $('input[name=target]'), as id is preferred for user scripts.
In general, ooui-ified items seem inconsistent as to what item get a unique id, but that's a ticket for after they're all done.
@Amorymeltzer I don't see this as needed. As long as there's no use case we shouldn't add code to be sent down to the client even if it might “feel” incomplete on a code-level. In OOUI you can assign a specific id via id: 'value' as config option or by calling setElementId for most elements (setInputId on InputWidgets).
I'd rather remove it elsewhere as well. Using ids is fragile, especially with super generic names like "target" that can easily appear in multiple places on the page (user-generated content can have arbitrary ids; it can't have arbitrary names). [name=target] is both more self-documenting and more robust IMO, and the performance difference is trivial (input field names are indexed).