It would be useful to be able to offer individual or multiple choice fields (based dynamically on member tags) in embedeable signup forms, in subscription CTAs from themes or in the modal portal, to be able to segment our audience more fluidly.
I don’t think, as has been said, that the multiple newsletter feature solves this problem, as we don’t necessarily segment on newsletters, even if it does provide an additional use case.
It’s possible to label members on signup. You’d need a custom form if you wanted to let your members select their own labels, but that’s possible now. What’s not supported is giving members any way to update their labels later. So it’s useful for tracking something invariable about members (like the form they signed up on), but not for preferences they might change.