Wilkerson getting the boot couldn't be that unexpected. He'd been hitting .232/.348/.304 in 56 AB's so far this year. He signed a one year deal worth $3M with $2M in incentives.
I can't really see why Nortan was designated. He'd been hitting .438 in 16 AB's. Nortan isn't sure of what he'll do, meaning that he isn't sure if he'll accept a minor league assignment. Nothing from Wilkerson yet.
As for Clement and Wlad, Balentien will become the starting right fielder for the Mariners with Wilkerson gone. As for Clement, he'll get playing time mainly at DH and some time catching. McLaren wouldn't say that Clement and Vidro would platoon, but Geoff Baker thinks that it will be Vidro against the lefties and Clement against the righties. Johjima and Burke's playing time won't be affected, but Vidro's probably will. Bavasi said that he didn't want to regret not calling them up sooner, so they brought them up now, hopefully for the better.