I own Siptah and I’m against this bullshit. I didn’t buy any DLC to own some exclusive contents but to use their contents in my games, be them singleplayer or multiplayer.
Speaking about multiplayer, it’s impossible to keep DLC’s content to DLC’s owner if the owner belongs to a clan. Since items and building belongs to the clan, every member of the clan can use them.
If eldarium is introduced to the EL, it’ll be the same if you try to make available only to Siptah’s owner. Non owner would be unable to use the recipe using eldarium, but it doesn’t matter if at least one clan member can use those recipe and craft items usable by all clan members.
Only singlepalyer could be penalized by this. But they wouldn’t since they can use the Admin Panel to spawn any ressources, materials, items and recipes from the game. I already do that when I want recipes from Siptah and eldarium to craft them on the EL. 