If IJ being down is a deal breaker for you then I wouldn't make a plan until a date is announced. We have our fingers crossed for the last week in April as my husband has never been on the ride before.
I hear you though! The Matterhorn has been undergoing refurbishment the last three times I've been to
Disneyland. I flat out told my Husband we would cancel our April trip if it went down during out up and coming trip. Haha.