I think you have a hard understanding that, whatever Wario and Waluigi truly are to Mario, they are not considered brothers. Having either one of them antagonists in a Mario Bros. game wouldn't make sense but having them be antagonists in say, a Mario Land game or a 3D Mario would be more expected.
I'm not disagreeing that Wario is irrelevant in general. I'm saying he's not appropriate for the Bros. series. Your idea is great but not suitable for a Bros. entry.