The Elsecalling Fabrial/The Messengers

[TacoBellChoutaMeal]

I re-listened to TLM recently, and I've got a few things I'd like to ask about now that WaT has come out.

1. Nazh tricks Nicky Savage and leaves Scadrial via what very well may be an Elsecalling Fabrial. Now that WaT is out, and we know that the technology exists, do you have any thoughts on that? Being able to enter and exit shadesmar wherever/whenever seems pretty useful, all things considered, but you'd think Navani would've had that figured out before we ever heard of Hoid or Nazh using one. The description of the thing doesn't seem super Rosharan either (iirc Sig notices the device uses a lot of gears). Could this be an invention from Silverlight? Do you think something like this will get brought up again when Isles drops in November? Or do you think this is a Threnodite invention? Both things would make sense in my mind. I don't know if Hoid is allowed on Silverlight, or if we know much about it. I just think the device might be interesting. 

2. The Coppermind wiki says that the messenger that  Harmony sent to MeLaan during her epilogue is its own thing and not a Seon. Are we sure about that? I had just assumed it was a Seon. 

[Epicdaf]

Are you talking about the device Hoid gives Sig at the end of WAT? 
I don't remember the specifics of it. All I remember was that Hoid gave the the dawnshard and then he was pushed into Shadesmar. 
I believe we are going to see some very interesting Fabrials or just technology overall once we get to Isles. 
Brandon has been teasing us with cool new technologies in his secret projects, so I am definitely looking forward for some very interesting Fabrials.