In fact, given that he starts the movie shape-shifted to look like Odin, I'd say his trickster bona fides come pre-proven.

Agreed!

I acknowledge that betrayal is strongly associated with Loki, due to the whole Baldr deal, but if Marvel were going to adhere to Norse canon that hard, Hiddleston's Loki should have changed sex at least once, had a horse baby, and invented the fishing net. (I will also accept the invention of fishnets, the manuscript error that everybody loves.)