Lewis Nethur

One interesting point that we can glean from the Sunlit Man is that space age Scadrians are actively searching for Investiture-rich worlds, embedding themselves into them (sometimes by trade and sometimes by force), and performing society-wide experimentation trials on them. With sixth of dusk, we had evidence that at least one band of rogue traders was engaging in such activities, but after Sunlit Man, it's clear that the behavior is systemic and very likely endorsed, funded, and contracted out by Scadrial's government(s) and militaries.
A second point worth noting is that Scadrians still appear to be fractured and tribalistic deep into the space age. This probably shouldn't be too surprising considering how actual humans work in real life, but it is worth noting. The female scientist who the Sunlit one meets in the vault seems totally divorced and dissociated from the horror of the experiments that they are conducting on innocent people, because she is; they do not seem to regard outsiders as "people." Historically, groups who practice that sort of belief externally also practice it at home. I would take this to imply that era 4 scadrial might have a functionally-unified military for defense and warfighting, but almost certainly won't have a truly unified government (Meaning that, tragically, the stratification, concentration of power, exploitation of vulnerable tribes, and deepseeded resentments leftover from Harmony's ascension may never fully heal within the entire arc of the Cosmere. And he was the extra-good, super-nice, double-Shard trying to fix the sins of the past leftover from the explicitly genocidal racist emperor who came before him!!! 😵‍💫 )
Lastly, (and much more speculatively) the great lengths that the scadrians go to in order to remain hidden, as well as how legitimately successful they are at avoiding detection while conducting globe-spanning experiments that could make nazis blush in embarrassment, is further evidence that they have done this before, on numerous other worlds both in series and in parallel. This means to me that either 1) Harmony (or maybe Discord) has completely lost control of traffic in and out of Scadrial and late-stage Scadrians are invading the rest of the cosmere with impunity for the purpose of rampant Investiture-exploitation (because...that is what they are used to having done to them and karma is an insane counter-intuitive b**ch like that...) or 2) Scadrial's scientists, engineers, and soldiers are responding and reacting against off world threats which are so grave and targeted that Harmony (or maybe Discord), the kindest and seemingly most well-intentioned of all the Shards, has given them his blessing and chosen to not take action to halt their coming and going (which he could presumably do at anytime like Autonomy).

The gemstones were originally added as ornaments, and it was only by accident that Shardbearers realized they could "bond" a gem-studded blade by maintaining constant (or near-constant) proximity/contact with it for a week.  Considering the context in which this is revealed in-book, by Jasnah to Shallan IIRC (EDIT: It was pointed out that it was actually Navani), I feel like it would've been a very odd omission for Sanderson to leave out that each blade requires a specific type of gemstone.  This tidbit would've been interesting, thought-provoking, not detracted from the narrative, and would've been somewhat relevant to Jasnah's investigation into the KR and the Voidbringers at the time.
Sanderson's style generally makes expert use of these short idle-conversations between characters to deliberately insert small world-building elements, which is what this would probably be classified as.  I would posit that since the perfect opportunity to make this reveal in an organic and logical manner wasn't utilized, it isn't going to be made in-book, even if it is a requirement.  It might be an interesting question to approach Sanderson with, and he might be willing to cannonize it, but I wouldn't expect it to ever be addressed onscreen.