In addition to what you guys said above, another 'barrier' for Little Mix is that a rock band like The Struts can tag along to a bunch of mini-theatre rock tours with other 4-5 small bands and rock fans attend. Little Mix would have to be the headliner, playing small venues for little kids. It's a very different approach. The best they can do is keep opening for big acts and continue to build a fanbase like that. Or give up and focus on Latin America and Asia.