I bought Dwimmermount last week, and just finished reading it. Absolutely beautiful, and gonna be what I run next, after the current campaign ends.
One thought I’ve had is porting over 5e’s backgrounds. Instead of branding proficiency to skill checks, however, they will cover a choice of one of two or three ACKS proficiencies. There would be no class restriction for these proficiencies, but the background would replace the normal ‘choose your own proficiency’ at chargen.
The main impact of this will be social, rather than combat, because aside from letting people pick class I restricted profs, I think the important stuff is in the backgrounds. Like the noble Background’s alternate, the knight, giving two squires, hirelings if not henchman, for free at first level.
Does anyone have any thought on how else this would impact the game, or any weird ways the rules would conflict?
I don’t see any problems with it, as long as you make sure to not let the players do anything crazy.
Some proficiencies are intentionally not given to some classes, mostly for stacking reasons (a dwarven vaultguard with Divine Blessing at 13th level, his worst saving throw is 3+). As long as you’re careful with things like Divine Blessing and Swashbuckling, I don’t foresee any problems.
I’m doing something roughly simila in my campaign. At chargen, you choose a land or region as your birthlace. depending on where you’re from, you get to treat three proficiencies as General proficiencies, in stead of class proficiencies.
So for example, the moon-worshipping Celenosi are guided by their Great Spirit (god, if you will) and receive visions often. They get to treat Commune, Mystical Aura and Illusion Resistance as General Proficencies.
Obviously, as Aryxymaraki point out, you want to be careful which proficiencies you hand out. But frankly, as long as everyone gets something, it’ll probably be fine.