Not yet, but clearly it is in trouble, based on this: Why Muji Is Struggling | News & Analysis | BoF.
My feeling is they have expanded past the point it is sustainable, and now they are going to have to adjust. Hopefully they can adjust: they are a good company and they could be as big as IKEA or H&M. Or they could go bankrupt. The next few years will show which direction they go.
Thanks to Jeff Smith for sending me this link!