If you don't think wakeboarders will allow it you are missing the mark, there is no way skiers will ever allow tricking to be replaced. Tricking is still pretty popular in the college ranks. I used to hate it, but then got the chance to watch Jimmy Siemers at the '01 Collegiate Nationals in Tempe, he finished a record run and then came back and did a raley on his trick ski, really pretty cool.
Back to the question though, their are a lot of older skiers with a lot of power with a hatred toward wakeboarders, they won't allow them on their lakes, or in their tournaments. Most sentiment in the skiing world is to not even allow a wakeboarding event, let alone replacing trick. I agree it could be good for the sport, but after running a college team for a couple years, I tried to spin a wakeboard team off many times, but I finally got the point that wakeboarders just really don't like to compete, they would rather hang out on the lake with friends and just ride, which is cool. I think that is mostly the draw to wakeboarding, it's fun to go out and do with a group of people, no one cares if they win a trophy, which is great. I don't even think there will ever be any serious talk of combining the two events. We used to talk a lot about adding wakeboarding into the college scene, but we have so many skiers, such as the Midwest Region's Dual Conference Tournament with around 500 pulls, that we can't add an event. NCWSA finally decided to let USA Waterski's wakeboard wing take over the collegiate sport, and now I think WWA has stepped in as well.