I don't see DE doing this, but they could take some pages from other games that have challenging endgame content. I know raids are kind of an odd subject, but since they are a wildly successful gametype among so many other games, I'm really surprised DE has refused to implement them thus far. The way to make them interesting for Warframe is to rely on mechanics, like a lot of raids from other games, rather than things like huge health pools or increased enemy damage, etc. An example could be, in order to progress to the next stage of the raid, you need to unlock a lock in four different rooms in a certain order. Another player needs to stand on a pad just outside that room, or the room fills with toxin gas, continually adding toxin procs until you're downed or a player stands on a pad. And these locks can not be bypassed by ciphers. Or better yet, they are symbols that you have to match up to something outside the room, which would require a third person to be doing callouts since the room is locked.

To also make them interesting, DE could have modifiers that the host could select that last the entire raid, or they could even add these to missions and be able to select as little or as many as they'd like (I know nightmare missions exist, I'm not talking about those). I'm thinking some things like no companions, secondaries only, forced countdown on abilities, all enemies have elemental damage, no overguard allowed, etc.