After re-reading TWoK, I'd like to propose the following theory on the origin of Shardplates and shardblades. During Dalinar's vision, it is shown that the world wasn't very advanced when de shard* were created. It is specifically noted that there are no fabrials at all, and it seems that there is not enough metalurgical technology to build someting like the shard*.
My theory: shardplate and blade is not build. Is is a consequence of the Nahel bond, on swearing the fifth oath. Moreover, I would propose that the shard* is the linked spren, acquiring a physical form. This would be in line with how the original shardplate appeared and disappeared almost at will (shown during the visions) of its wielder.
Moreover, this is also suggested by several scenes we are shown: the effect of Dalinar jumping down with his shardplate is very similar to when Kaladin jumps down while light-infused, also we have a couple of scenes where Syl was "protecting" Kaladin.
This would also explain (or be foreshadowed?) by Kaladin's reluctance to take the shards when fighting for Alamar... those are not *his* true shards, and in fact, as they were abandoned by the original wielders, they probably have lost not only some of their powers, but the connection with the ideals and spren that gave rise to them.
Another note: we have that fabrials are built by somehow "trapping" a spren into them. If the shards are built according to this theory, they already have a built-in spren...
What do you think? Might this work?
