I gotta say not a huge fan of bringing in a '7th' magic to be totally honest. Especially if it can cover the 6 types already introduced. I do like the concept of runes on the other hand however.
Maybe if the runes could only cover basic spells of the other magics (e.g. shoot fire from one, maybe collapse the ground with another) it mightn't be too bad. I mean I can mostly see runes being like 'magic is cancelled within five meters of it being placed' or 'a magic barrier is formed around generic distance' sort of thing more than being any of the elements.
Which in of itself is a different issue, but that just me running a mage speaking XD
I mean if the runes could summon a tsunami that would be a huge issue (not that I expect them to), or if it was to flood a room with lava/fire. (Then again I think of 'mine' runes and they would be hilarious XD)