I don't think Binance will be able to beat Bitmex in terms of margin trading. Remember Bitmex has been in it for long thereby having a very large community in fact can be likened to be a top margin trading platform. Although, Binance has a large community already but it's not in terms of margin trading. With Bitmex continuously improving their platform and Binance just coming up, it will be hard for Binance to overtake them.