Realistic facial hair designed to fit the noob head template, with various colours to choose from. There was already a beard sold a little while ago (around when Destiny was released), and it actually looks pretty good.

There are a huge number of possibilities with this and I don't think any of them could really be considered reused ideas, as long as the style is even a little different.

This is a bit of a bigger idea, but there could even be a dedicated shop that sells hairstyles, including facial hair.