For Kpop to be truly mainstream in the US, the "K" will have to be further diluted using phraseology from Hitman Bang.
A big factor in Kpop's success to date is the lack of local competition (bg's and gg's). But the dependent nature of relationships with major labels have both helped and limited the expansion efforts of the Big 4. Plus, they have to cater to the domestic market as well.
As the major labels see the demand and want in on the action, the next step is a test of the localization strategy in the US that Kpop companies have used in Japan and China. This is already well underway with JYP's x Republic's A2K and HYBE x Geffen's global gg joint ventures.
It remains to be seen if Xpop can become mainstream - whether the breakout group will be a Korean based global group like NewJeans or XG or a homegrown one if technology is shared and the tech transfer is attempted and completed. Once technology is open sourced, crazy things happen.