out of combat move speed works great to roam around the map and play the vision game.
the changes to dusk blade are awesome for a support! you get alerted when walking over a ward so you can easily clear it, but even better it disables the ward for 8 seconds! so if you have knowledge of where the enemy has a ward then right before your friendly comes to gank you can go deny vision by walking over it and helping the gank succeed
your in the front line, a spell shield is a good thing to have. plus its good engage if you time it well as you Sion Ult in the shield with be ready right after you land your ult.
move speed boost is not bad. don't need this as much for support but is nice to have item for any off meta AD supports