Had a discussion with you lads about higher difficulties on stream a couple weeks ago, solid points from everyone in the team that was there, and I understand why a higher difficulty isn't in the books.
That said, I still believe in my heart of hearts that it would add longevity to the game, the numbers may not be big today but the way I see it, players are always improving and so the amount of greybeards is ever-increasing, higher difficulties also motivate people to improve further. I imagine greybeards also drive the word of mouth quite actively which is why keeping them around with a challenge just seems like a good investment to me
Totally not copium
(I know mods are one way of doing it but let me tell you I'm definitely not interested in what OP posted, scout with thunderhead and just flooding the map with 8000 spawns isn't my cup of tea)