Originally Posted by
Grunty
It might even be the opposite of "shocking" for anyone not invested in the Otherworld/Excalibur side of the X-men, not only in the current "Y of X" era but X-men in general.
With the X-men franchise often offering a bandwith of different series with different themes, nobody should be expected to be a fan and/or reader of everything. Therefor it should always be considered that a majority of readers only has limited knowledge of all events going on during a status quo (in turn another potential problem with the current status quo being a "everything in the same pot" situation).
This series was not hinted to have any connection to the "Excalibur corner", which has recently gone without success for the 2nd time, featuring a world and set of characters divorced from it. So to throw a character into the main villain role who's recent importance was entirely tied to only that corner, means that rather than shock, her appearance might have easily just caused a unenthusiastic "who?".