Trell is a shard we have seen before. Threnody does not have a shard on it, but it may have at one point. I propose that this unnamed shard wanders the cosmere destroying planets. Its metal is a spike that brings spiritual things to the physical, like spiking shades turns them into physical beings (red-eyed faceless immortals). This theoretical metal could also explain quite nicely how Kelsier got his body back. In the BoM broadsheet, the main story of (Allomancer Jak's woman friend, whatever her name was), she was fighting a guy who had a gun that charged from green to red, and then disintegrated a window. This might be weaponized threnodian technology. Using a story in a broadsheet as hints about future books has precedence (stories about encountering masked savages in the SoS broadsheet), and when Main Character Girl goes back to investigate the wreck of the skycar she is met by a "thin, white haired, young guy" who asks her some slightly mocking existential questions (Hoid?). The only way Hoid? could be included is if this story is based on actual events (the only reason to pay attention to a fictional newspaper story).