I have a theory. I'm not sure if there is a WoB that renders said theory inert, but I figured what the hedge, it wouldn't hurt to get the opinions of the mortals.
What if you could lash Shardplate? First of all, would it even work? I don't believe there would be a reason why it wouldn't, unless the Shardplate's magical properties somehow make it were Stormlight can't be used against them.
But think about it, You could lash a Shardbearer to the ground, tripping him up. You could lash him to a wall, so that he becomes immobile and can not fight you anymore. You could Lash him to the roof, and presto same as Lashing him to a wall, with the added bonus of him becoming confused as hedge.
I realize these are already things you that we know one can accomplish with Stormligh, but as far as we know they have not been attempted against a Shardbearer. Additionally, there are two other uses I can think of for Lashing a Shardbearer. You could Lash him into another enemy, this would push the Shardbearer off balance, and could seriously injure or kill the other enemy if they are not also wearing Plate. The other option I could think of is Lashing Shardplate off of its bearer. Maybe not all the pieces at once, but if you focused all of your concentration onto one piece of Plate, such as the breastplate, then possibly it would succeed. The bearer would be fighting, impervious to injury and then all of the sudden his chest and stomach are exposed for a killing blow.
I don't know. Someone with more Rosharan knowledge (sadly I don't get nearly enough of it here in Camorr) should tell me if this is possible or not. Also, if you do think it will work, can you think of any other uses for this technique?