Warframe has always been a big, fast game, focused on speeding through levels as the proverbial sanic space-ninja murderising ALL THE THINGS in an orgy of mayhem, power fantasy and particle effects.
Then they started introducing world-boss type things like the Eidolons and the Orb Mother etc. Personally I'm not really a fan of these things. They're not perpetually available, which means you have to do it when it IS, rather than when it's convenient for you and, by and large, they're long, repetitive and (after the first few) really, really tedious. I don't enjoy them, but I accept that they have their place, and that there are people who do.
Personally, I'd *LOVE* to see a mission-type / map-group based on an Infested tile-set... but not a Corpus/Grineer-taken-over-by-Infested thing, but an actual pure straight up Infested only set. It could have really tiny, narrow corridors, creating a claustrophobic Aliens/Space Hulk like vibe as you're hunted through the tunnels by uber-scary nasties while trying to achieve whatever the mission goal is. It would be even better if AoE-spam was restricted to the very limited sightlines, so you couldn't just run through with an Ember or Saryn nuking everything that can't see you. I know it's not particularly "Warframe-y", but then I didn't really think the world-boss things were particularly "Warframe-y" either, so what do I know.
I just think it would be great to have a mission type that relied on resilience, toughness and non-spin-to-win melee (maybe make those weapon/shield combos useful for a change!), rather than tearing around in invisible nuke-frames all the time.