Do you think Goth has become mainstream? No, at least not in the US. Goth aesthetics do cycle through the mainstream every few years, but they are used as marketing gimmicks, an injection of "street cred", or used to give flair where people are looking for the next big fad. While I think goth is on the whole more accepted in the mainstream now than in days past., If not by persistence of participants then by the proliferation of much stranger niche cultures the internet has made accessible. I also just don't think the core and spirit of goth is something that would ever be appealing to a mass market.

Is there tension between older more traditional Goths and those from newer Goth groups? Yes and no. If we look at people who were around in the early 80's and watched the goth scene evolve, I have found they either don't really associate with the word goth, or if they do, they are generally OK with the state of things other than fashion trends like nu goth, pastel goth, gothic lolita, etc. Where I find the tension usually lies is with the deathrock/trad goth crowd, who tend to be younger, maybe coming into the goth scene at the mid 90's the earliest. I think they've sort of idealized the early 80's as pure and the real goth (even though it wasn't called that). For them goth is often considered to be fashion and music and nothing else, so not only do they dislike industrial, Victorian goth fashion and sometimes even the new romantic or glam look, but they don't see goth as having a lifestyle or ontological element to it. It's almost a punk mentality. So then you have the newer gen. that doesn't know much about the history and may be into stuff like witch house, more of a nu goth or mall goth look, and the trad goths who have idealized the old days without accepting any iteration or evolution past then, and there is a tension there. Of course you will have assholes in both camps (I don't use the word elitist because I think that can be a positive thing.) I personally take a more moderate approach. I think we need to know our history and stay true to that, but also not be afraid of change, it's certainly a tight rope walk, which is why there is that tension. People hold goth as a very personal expression and want to protect it, and I think that's great and that discussion, when civil, is necessary.