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I guess if the shardplate/blade is a piece of a dead spren, it'd make sense if it gave either whatever powers that spren would've given the radiant?

I'm fairly sure that Nale doesn't have an honorblade, as when he's fighting Lift in the final passage it says that he attacks her with the blade in the form of an axe, and from Szeth's reaction to Kaladin's spear it's clear that honorblade's can't transform like that. As for the implications of that, it means he must've bonded a highspren but as for how and when and why I don't know