I really think Automaton Tower was the answer a lot of us were looking for in PvE content. I've said it over and over here but they finally developed some challenging content for people to build for, on a monthly basis, and then nerfed the hell out of it to the point it's another auto mode. The solution wasn't a nerf, it was a different distribution of rewards. The E7 community is a little skittish when it comes to challenge to the point they complain so much about hard content they can't beat day 1 until it is nerfed. Latest being Nilgal.
I'd love to see some massively ramped up difficulty where the rewards are purely cosmetic. It gives you something to strive for and then you can show it off in PvP, your support units, your frames, etc. Stop locking the most desirable currencies/equipment behind the hardest content and people won't complain as much.
PAD has an excellent set of monthly challenges, a game I've been playing for years, that I still can't complete each month and/or takes serious team building throughout the month to get through. The reward for the final challenge is equivalent to like 5 covenant bookmarks though. Or PAD's ranking dungeons where really only the top tier players get the equivalent of SSS rank (think like trials) but the reward is a crown that does literally nothing but go on your nameplate.