What I would consider to be the most pure of RPGs are definitely niche at this point.
The first signs of RPGs becoming more mainstream, back in the late 1990s, were really the result of the games, in a sense, becoming less pure. In terms of JRPGs (like Final Fantasy 7), you have games putting in a heavy focus on story over gameplay, with excessive amounts of cutscenes; this is also when minigames (almost all of which are not RPGs) became common in the genre. With WRPGs (like Baldur's Gate), the game has moved away from being turn-based, and you also see some rather complex dialog trees, which feel more like the sort of thing that would fit better in a visual novel or adventure game.
Even later, because people complained about the random invisible encounters common in JRPGs, developers started making the enemies visible, but had them move in real-time, which again makes the game less "pure". (One counterpoint here; the SaGa series has had visible enemies moving in real-time since the Super Famicom days, and that series is generally considered niche; as much as I adore that series, the visible enemies moving in real-time is actually one of the things I *don't* like about the series.)
So, "pure" RPGs, as I am calling them in this post, are a niche genre; those that adopt aspects from other genres, often at the expense of their RPG-ness, are the ones that tend to be more mainstream.