We do hear the request for higher difficulty levels intermittently, and though there's a few people on the team who'd like such, personally, I'm really not a fan. Invariably they'd just be giving random bonuses to the AI & maluses to the player - that's all the easy difficulties do atm. And tbh, that feels like a cop-out. It's not really making the title harder, it's stacking weights on the backs of players.
Which, y'know, might sound fine, why not let people opt in to that if they want to? The answer there is because nothing else in the title accounts for that: costs are not designed to be variable in that way, systems are not designed to account for those types of sliding brackets, the AI isn't set up to cope with that level of variability. Some costs'd get dialled up, and in exchange, some parts of the title would likely break, some would quietly bork their balance in a way that's basically invisible to anything but dedicated playtesting in that specific area, some would
kinda work but feel wrong, and so on. We'd be giving you a button to break your game labelled "harder difficulty" and then shrugging our shoulders at you when you press it and it breaks your game but doesn't necessarily make anything all that much harder.
Of course, we could sit down and rejig things till that's not the case. Definitely not impossible, not even technically, but it's a
lot of potential work to both make and maintain forever. That work doesn't come out of nowhere, it's an opportunity cost that we do instead of other things. Do we put 2 months, 4 months, 6 months, 8 months worth of development delay in before the next DLC so that we can add that game rule and have it meaningfully do something rather than be a placebo that's also a secret mild poison? What do we get out of that? What does the playerbase get out of that, including the harder difficulty fans, who I suspect have other things they
would prefer ahead of said game rule?
Turning difficulty down is easy. We turn some things off, we reduce some negative modifiers on the player that new players won't have headspace to grok straight away. Turning difficult
up in a meaningful way is disproportionately hard.
Ok, that's a lot of doom'n'gloom, and I didn't really mean to dump on you. So, to try for a bit of positivity, the type of difficulty I
would like to see added to the title is meaningful friction, meaningful setbacks, and better AI. These are all much harder to do, both to actually make and to get dev time for, than small tweaks, but various team members are working on 'em. I'd like to see more ways for characters to die unexpectedly. I'd like to see ever-tighter war AI & more difficulty for the player wrangling their armies in war. I'd like to see the AI get better at the economy so that player snowballing is less of an issue, because the AI is snowballing alongside you. I'd like to see more nuance to factions and ways for them to destabilise your realm. I'd like to see ways to break up blobbing that don't make people ragequit. We've done some work on some of these for this release, some for upcoming patches, some are planned for the future, and some are just glorious dreams that I drunkenly ramble about at work drinks to anyone who can't find somewhere else to sit. To me,
this stuff is difficulty, and it's a much better use of time than us chasing a working set of difficulty modifiers.

Just my two pennies.