So while reading through Way of Kings again, I devised two theories, and would love some input:
Thought number 1: Spren make up shardblades once the surgebinders have said the right words. In Dalinar's visions, the Radiants also have plate, but Szeth has said he can't wear plate or it will effect his powers. I believe, once more words have been said, the Spren will also be able to make up plate, eventually uniting man with Spren.
Thought number 2: During an interlude chapter in The Way of Kings, we find out that spren, once measured and written down, cannot change that measurement. What if, someone, during the day of Recreance, the spren that made up the knghts Radiants Plate and Blades were somehow measured, freezing them in their current state. The Knights Radiants could no longer hear or interact with their spren, probably even suffering from touching them, as Kaladin would suffer touching a shardblade, and this is why the abandoned them. Also, now frozen, regular men could use them. If this is true, I am thinking a major plot of the series will be to rescue these spren. To find where they have been recorded, and erase that, freeing all trapped spren in the Plates and Blades, perhaps allowing even more members to join the Knights Radiant.