I'm not too keen on the whole idea of this feat. It seems inappropriate to given commoners full access to true magic simply because they have elven blood somewhere in their lineage. The ability to use elven magical items maybe... But the ability to use elven magic without being an elven mage not likely, especially not through the use of a single feat. The art of magic requires lengthy and repeated training. Once wouldn't simply learn elven magic without spending time in communion with the elves and being taught their ways.

The whole concept just doesn't fit my style, but that doesn't mean its a bad idea. :)