Somewhere to properly store thinks like picks, extra strings, cleaning rag, toolkit, music books and especially the guitar cord would be nice. And the outside of the case should be smooth so you can put groovy stickers on it.
It should have a sturdy lock and a way to secure it to something else so it doesn't get stolen. A GPS tracking device would be cool. Metal corners so it doesn't scuff.
A hidden compartment would be kinda cool too...for uh...stuff. A built in bottle opener. A way to convert it into a music stand. And it should be pre-worn looking so new players don't look like total dorks the first time they go on the road.