I've been racking my brains trying to think of any viable groups that could possibly do this.
Literally can't think of any with enough success to warrant it. Cleopatra I guess but given that they are sisters I can't really see there being much of a story to tell, and there isn't a "reunion" aspect to it. Similar with 3T last series who were so boring they didn't even feature that much if my memory serves me correctly.
I can only see a watered down S Club Juniors, or groups which have remained active without much UK exposure such as Aqua, Vengaboys.
Unless like others have said they're looking to more recent acts such as The Wanted and JLS? Even then I'm struggling to think of anything else realistic.