At first I thought having Lana Lang and Steel’s daughter from the future come back in time a be Supergirl a good idea, but that’s way too redundant. It’s too similar to Cir-El. You may as well use her instead. I wouldn’t mind Cir-El coming back.
Linda, if she ever came back, would be more a Superwoman than a Supergirl.
But I can see DC doing what they did with the Future State Flash: bringing a different Supergirl from the multiverse and putting her on main Earth.