Hmm, yeah, per Cid, that's not EXACTLY a spoiler, except for possibly the part where it's actually Earth wut. Didn't know that, actually, my distrust in books past the first 7 is based on hearsay, I didn't actually read them... although the fact that I eventually realized I disliked Talismans of Shannara fueled my lack of interest in seeing a continuation. My recollection is that there's the usual hypertech civilization that existed in the past but without magic but it got blow'd up, and Allanon hems & haws about there being some great cycle between magic & technology, and it's a plot point in Wishsong that the era is turning and all the magic would be dying out and an age of technology was to come (and that this is established early so isn't even really a spoiler).
Then in the Heritage books (Scions, etc.) 300 years later this is thrown in the garbage and his ghost says something like "magic leaving is horrible we need maaaaaaaaagic" which would be sort of acceptable in the sense that obviously the book series would be over, or at least very different, if they went with a low-magic world, except that the very plot in Heritage seems to contradict this (rogue magic turns people into Shadowen who are just evil 'cuz.) Unless they want to claim that mages would gather up all the rogue magic and prevent it from turning evil or something?! Who knows. (I'd have been happier with "some evil force is undoing all that wheel turning crap and bringing back EVIL MAGIC, we need to marshall up good magic to stop it" or something.)
Dhyer: The market worry doesn't seem necessarily true at all. The very point of all those 80s nostalgia remake movies is to drag adults into the seats due to nostalgia & kids because they're the target audience. "Transformers" or whatever certainly got current kids as well to watch it. Granted, sometimes the kids don't show up, but that's usually a sign of general failure (e.g. Speed Racer). To a lesser extent, the same with superhero movies... although superhero comics does seem afflicted by that problem, the main market that buys physical comic books seem to be hardcore adults who never outgrew it.
Also, a Mistborn TV series would be quite expensive to produce. Less big expansive royal processions than Game of Thrones, sure, but lots of intricate action scenes. You could do a very talky Mistborn but I think this would miss the point to a degree, I'd think the main selling point would be expensive fancy fight scenes. (Certainly the dialogue in the books is nothing special, even if the plot is decent.)