Never. This is a terrible idea. It is terrible in tabletop games where everybody wants a subclass of fighter so they don’t have to take the downsides of other classes. Swordblade, arcane archer… we don’t need it in WoW, we have a ton of class crossover already and anything we lack can be done with a new class instead of making another system arbitrarily worse for little gain. Look at hero specs… that is about all you would get.