VK'll never be really popular in the western world if there isn't a western scene to begin with. What there is are western fans of a Japanese indie music scene, but there isn't something you'll heard and say "That's your typical Western visual kei", a V-rock adapted to western tastes. (Which is never going to happen because most fans are a bunch of elitist who are still crying about the old times™ and shitting on every band that 'dares' to be VK outside of Japan)
And, really, when was it actually popular? Never
Yes, there was a JFashion trend in the 00's that made a lot of people interested in the scene, but it was all people who was already interested in Japan (culture, language, anime/manga, etc).
It's always been a niche thing, weird music weird people listen to, and will always be.
Nothing that comes from Japan will ever be as popular as K-pop, simply because Japan's attitude over what it produces is completely different from South Korea's
Korea's been putting a lot of money and resources into making K-pop and everything related to de hallyu a popular thing worldwide and even trying to make K-pop an international genre that stands on it's own by attempting to make groups outside of Korea
Japan, on the other hand, is pretty much content with it's own public and cares little to nothing about having an big fan base overseas.
Now, I want to know: Does it really need to be popular? Why should it be? What does visual kei have to offer that would make it stand alone in the Western mainstream media?
A bunch of people weirdly dressed people playing some type of rock? You've got a lot of those already