So, the (extremely amazing) DK music that was uploaded today got me thinking...before now, there hadn't been a sample of DK music on the site. And no series has gotten more than one sample since the site went live.
What if--and I'm in full conspiracy mode here--what if every series is intended to get one sample track, and they're holding back certain ones to coincide with newcomer reveals? Full newcomers, not echoes, I mean. It might be a stretch, but it is possible.
And guess what series suspiciously doesn't have a sample yet: that's right, Super Mario.
I find that odd. They started with the Smash theme, Zelda, and...Street Fighter? Why not just use a Mario remix? We already know there's at least one: the SMB3 Bowser battle theme, used in Bowser's info video. But they haven't uploaded that one, or any other Mario arrangement, this entire time.
Could be coincidence. Could be they're holding off for Geno. Until they post a Mario arrangement though, I choose to believe the latter.