The following piece of concept art apparently hails from a now deleted Image Shack account (not dissimilar to how that large batch of artwork from the movie found its way online recently). As you can see, it features a Sith villain from Star Wars Episode VII, though whether this is one of the character's we've heard about or someone else altogether obviously is unclear at this point.
As you can see, the lighsaber appears to have two smaller blades near the base giving it the appearance of a sword (possibly to stab opponents up close). As always, take this with a pinch of salt for the time being as there's always a chance it could be fake. It certainly looks legit though!