So, as a starting principle, Ibwould maintain "modular" backwards compatibility with 5E: nit necessarily keeping things the same, but working the math to ensure that people could bring 5E characters to a 6E table without causing disruption, or use 6E characters in a 5E Adventure without needing to recalculate anything. So, nothing radical on the gut level. More specific changes:
- "Races": I would take Tasha's approach to Lineages, and bake it in Core, and push it forwards a bit: make it easy for a DM and table to add in new Lineage options based on a player's ideas or the needs of the world.
- Replacing "Subrace" with "Culture," so that every PC mixes a Lineage with a culture, which cab be mixed and matched: Halflings raised by Dwarves, urbane Goliaths, etc.
- Backgrounds: I appreciate that they are mechanically perfectly equivalent in 5E, and I would like to keep that. I would take more of the fluff from some Classes and put them into Baclgrounds that are Class agnostic (looking at you, Monk).
- Classes: I would keep the current 13 Classes, promoting the Artificer, but some would receive significant changes: de-Orientalize the Monk (Mknasticsm is a Background, anyways), rebuild the Ranger extensively (make the usual Subclass choice be based on Favored Terrain: Underdark Rangers, Forest Rangers, etc), etc. Make every Class choose an Archetype at Level 1, which leads to
- Themes/Archetypes: Replace ""Subclass" with "Archetype" or "Theme," based off of the Strixhaven UA: many if not most Archetypes could remain focused on a single Class, but allowing for cross-Class options built into the system would be amazing (maybe based around Fighter-Rogue-MU-Cleric groupings). Allow a Fighter or Rogue to take Ranger Archetypes to have a "non-magic" Ranger, or have Fey Warlocks and Fey Sorcerers key off of similar abilities.
Other than that, wouldnchange much at all.