I had some ideas not just about classes, but about subclasses in Avalon, and what I would tailor. More than happy to get @Fafhrd’s opinion on this as well.
I looked through all of the “official” D&D resources, as well as throwing in some of my favorite 3rd party items as well, like the Max Press products from Robert Schwalb and the recently released Seas of Vodari.
I left subclasses of the list for anything that made the magical feel too “well known,” so anything that implied familiarity with the supernatural on a regular basis (at least regarding entities), and anything that introduced the supernatural to a class that has a baseline of not being a spellcaster or supernatural.
I pulled Life and Light out of the Cleric domains, not because some of the religions may not preach those things, but because the tone of those Domains feel a little more “modern-day” heroic, and I thought removing them as options reinforced the grimmer tone of the setting.
I actually wanted to remove some of the traditional schools of magic from the wizard, to remove it from the “known” way that magic is organized into schools in D&D, but given that some players may only have access to the core rules, I didn’t want to remove too many options for wizard players.