The three main complaints my past players have had with ACKS are that mortality is too high, levelling is too slow, and domains are unsatisfying. I hope that they will correct me if I am wrong. I will be blunt - my intent is to make ACKS somewhat more forgiving. Not as forgiving as 3.x, but a healthy compromise.
Mortality is tricky. ACKS is pretty good about making the consequences of death sort-of-mitigatable, but my understanding of the concern is that sometimes you roll some really bad news on the RL&L table and then you pretty much have to retire. Certain results are vary wildly in their punitiveness based on the receiver's class, like the move-silently-is-impossible and the reduced divine spells per day. The Invisible Stalker is widely regarded as an infinite re-death sentence, and the blindness and reduced con/wis results are also considered retireable. One solution, I suppose, would be to give a global bonus to RL&L and mortal wounds rolls - one option proposed on the forums was +5 to mortal wounds and -5 to RL&L for a gritty, Iron Heroes-esque campaign. I could see giving a bonus, maybe +3, to rolls on both tables. This would push you up half a category on average, making the really miserable results less likely but not impossible, while opening some of the 21-25 results as more possible. Add in point-patches to the invisible stalker (maybe it's willing to bargain) and the move silently and we might be in business.
Another option would be to allow some movement between the d6 and the d20 results; maybe you can subtract 2 points from the d20 to add one to the d6 or subtract 1 from the d6 to add 2 to the d20. This would actually give players some choice in the matter and lead to some lesser-of-n-evils type decisions, as well as permitting them to choose afflictions most in keeping with their conception of their PC's nature.
Ultimately the problem with the death and dismemberment / tampering with mortality tables is that they, like critical hits, hurt the players a hell of a lot more than the monsters.
Moving on to levelling. One option, as I have mentioned previously, is to increase treasure yield. I still think this is a good one. Part of the allure of the OSR for me as a DM was that I could give out so much loot the party would need to bring shovels and mules to get it out of the dungeon. The tables, however, have had other ideas. Magic gear is also how you incrementally get new abilities outside of the quantized levelling structure, so more treasure helps there as well.
Other options: global percentage bonuses to XP like prime reqs (but then you can't afford to domain when you get there), inter-season breaks where people acquire gold and XP off-screen. Smaller parties wouldn't hurt either. One thing I have been considering regarding domain XP specifically is dividing your GP threshold for the purposes of some income by the number of people you're splitting that income with in order to make shared domains more reasonable (ie, 5-man party gets a domain and divides its incomes. Normally nobody gets any XP. In this case if your XP threshold were 40000 GP, you'd treat it as 8000 GP for the purposes of income from that domain, because you're splitting it five ways).
The domain problem is under ongoing investigation, both through reverse engineering and reading other sources, as discussed elsewhere. More to follow in further posts.