From the News and Discussion thread:
Borys Kit @Borys_Kit 1h Following up a bit on @DrewAtHitFix's take on Quicksilver: Heard that Fox can actually use the Quicksilver and Scarlet Witch names...
Marvel can use the the names Pietro and Wanda.
Also, to insert the character so late in the game (X-Men is already shooting) is Fox's way of asserting the character and a dig at Marvel.
This doesn't give much hope that "Quicksilver" is going to be a deeply fleshed out character.