the idea of chipmusic as mainstream/public comes down to what you define chipmusic as, which is probably an annoying thing to say considering that hella people have said it already
honestly, the only way to think about chipmusic (aesthetically) as being underground/not mainstream is to stick to the idea of a chipmusic medium in that you're still composing on video game hardware. it's an easy label for outsiders who need to categorize this kind of music, but it's a really terrible label for us as musicians trying to parse our way through it because it's a label that doesn't refer to just the aesthetic NOR the method of creation. aesthetically, it's mainstream, medium-wise, it's not, culturally, it is/isn't? it's just a tough label to work through.
I guess it's just really surprising for us (or me) because they've already embraced what chipmusic as a culture is just getting to grips with -- namely, video game hardware NOT being in the center of the music's image. it's like a simultaneous crossing over of us into mainstream-ish territory and them into underground-ish territory.
kind of like when that britney spears dubstep song dropped! all the dubstep heads lost their shit because their image of dubstep music being underground was shattered when the aesthetic got rebranded as a "Britney Spears song with dubstep in it", instead of a "Dubstep song with Britney Spears in it." when your aesthetic isn't the main idea/image/thing being portrayed in the music, you've become "pop" music. replace "dubstep" with "chipmusic" and you've pretty much got the same thing happening.