Opening Disclaimer: I'm sorry I'm not going to have the exact references directly in front of me, but my Dad has my copy at this time and is a slow reader.
The part of Shadows of Self that really caught my attention, was the fact that MeLaan gave Wax his earring personally, on what I assume were Harmony's orders. It is confirmed as being a Hemalurgic spike, but the ability that is charged with the spike is unknown. My theory/hope is that the earring is the same earring as the one Vin wore during the original trilogy (giving it an allomantic bronze charge). I saw a post on here about the earring before, where the poster theorized that the earring has a pewter charge, as Wax is seen to be strengthened by the mists. Well, during HoA, didn't Vin become the Mists when she took the Shard of Preservation and drew all the mists into herself? Could she be giving him a slight physical boost as she did to Elend at the end of HoA? One of the things that made me think this (I'm really sorry about the reference part here) is the short aside from Wax in SoS where he talks about a form moving with him in the mists sometimes. Furthermore, in several sections of the book he muses about Vin and what she would have been like, but what if she is really the form in the mists that he can sense when he is about? Here is where I think about how Vin was able to sense the Mist spirit using her bronze, and maybe the Bronze allomantic charge of his earring allows Wax to be able to sense Vin in the mists.
Partially related to the above theory, but how is an allomantically charged hemalurgic spike used? Did inquisitors have to actually ingest the metals they needed before using the abilities, or did the spikes themselves provide a certain measure of the abilities? If they needed to actually ingest them, I could imagine duralumin steelpushes being very dangerous for inquisitors, as how could they see after doing something like that?
(First post, Sorry if not put up in the right way)