First of all, very nice to hear some bluegrass music played by real musicians (or a VERY good job tweaking samples)!
The playing and recording are top notch, but here is what I personally thought I would change:
• The panning of instruments. Right now you have three pan entities, and the sound kind of jumps left and right between the banjo and the lead guitar. This can be a tad bit distracting if used as background music.
I would double the strummed guitar (Hard L & R with a real second take, or by faking it) to have a more modern, wide stereo image, and have the solo instruments sit in the middle.
• The composition. While it’s nice, I would make it a bit more exciting. Raise the tempo a bit, and maybe try to come up with a less improvisational song structure, even though it’s bluegrass. Maybe a more memorable hook lick or a clear chorus section?
Anyway, it’s of course a very nice track, but to make it really commercial, those are the things I would change. But that’s just me.
Best of luck!