The lore seemed conflicting until now so at best we had "references" and "inspiration" as you said. In the new Warframe 1999 light however, it seems like it could just outright be... true, and this glaive did actually exist before the orokin empire.
Well, even if Dark Sector has been made by DE, the IP is owned by Deep Silver so I don't see how they could integrate the game to Warframe's lore without risking a trial...
I'm sure DE's lawyers have done a lot of research about how far can they push it before its infringement, I'd say as long as they don't use specific names, assets or story from dark sector it should be good. Or alternatively they can maybe even buy back the rights if needed, who knows
Just like the Xeboblade/Monolith situation where fans expect Xenosaga to become cannon in the Xenoblade universe after a 1 minute video they over interpret without concerns about the legal and profit part (Xenoblade is owned by Nintendo, Xenosaga by Bandai and Nintendo would never share the benefit made on Xenoblade just to make fans happy), we have fans expecting the fusion of Dark Sector and Warframe with an over interpreted video of 5 minutes.
Like you said DE can create something similar without it being Dark Sector. That would be a more logical thing they would do based on law.
Unless we have a wall street news that announce that the IP change hands or that Tencent now own Deep Silver prior to that trailer (because not doing it in that order could be consider a market manipulation that would be sanctions by the FTC) the only possible outcome stay the same as before: Dark Sector and Warframe are 2 differents things.
I would prefer Tencent to disappear. It has become a way too big company to not be concerning and even if they saved Warframe by buying DE, I think on the long terms it's better for icarus to fall...