For this to be a major problem, there has to be a large group of website owners, large enough to be enticing to other browsers, who both accept tips in BAT and are reluctant to accept tips in some other, additional cryptocurrency, and Brave's owners have to be able and willing to shut other browsers of BAT tipping, no? It doesn't look likely that all those conditions will be fulfilled, even assuming that that critical mass of BAT-tip-accepting sites is coming or is already here.