You'd think DE would have been enough of a 'test', if that were the case.
DE proved that they can take an ancient, ugly, unpopular army and turn it around into something fun, functional, and aesthetically pleasing that loads of people want.
Sisters would require less work than that, even.
They're less popular than DE were, but I don't think it would take much to make them at least as popular as other mainstay armies.