On their FAQ page, it mentions future plans to offer utilities for bands to sell downloads, create and sell merchandise, and sell concert tickets. Presumably, those would be pay services. (They could also sell premium packages that allow artists to put up more tracks, get analytics, etc.).

I mean, this is all conjecture, but figuring out the business model for a site like this doesn't seem too difficult.

Whether or not indie bands will pay for that sort of thing, and how much, is a completely different issue.

Looks like there might be some planned synergy here between muxtape and Normative, Jakob Lodwick's music label. Reggie Watts--one of the featured artists--is signed to the label, and Lodwick is an (the?) investor in muxtape.