- The six standard ability scores? Cut down to four. Strength kills Constitution and takes its stuff. Intelligence, Wisdom, and Charisma get broken apart and reassembled as two ability scores. Shadow of the Demon Lord already does this and it's smart.
- No numerical ability scores, just the bonus/penalty. The numerical score is already a vestigial tail that barely sees any use in the game; the time has come to jettison it.
- Races would have a whole lot less in terms of features because they tend to include a bunch of cruft that is quickly forgotten about in play. One or two spiffy features, maximum.
- Ability score increases would be decoupled from race choice, or at least remade as a potential source of ability score increase among others.
- Tabaxi and warforged are core now. Sorry. (Not sorry.)
- You make the subclass choice for your character at 1st level now. No more waiting until 3rd level to play the character you want to play. You wanna play a beast master ranger? Now you can from 1st level. You're welcome.
- Classes will only be detailed up to level 10 in the Player's Handbook. According to the available data, 10th level is about the highest level people tend to play to before their campaigns end anyway. Higher levels can be their own book later on, which will give that stuff time to actually be playtested.
- Milestone XP is now the default. Totting up XP as homework is hereby abolished.
- Alignment is gone. You won't miss it.
- Backgrounds stay. That shit slaps, as the kids say.
- The skill list can probably be pared down just a little bit more, especially if we make mix-and-match skill plus ability score a core concept. Do we really need perception and investigation?
- Bonus actions are gone. We can do better.
- More emphasis on reskinning the fluff around mechanics to get your desired game aesthetics.
- No default setting. The emphasis will be on making your own setting.
- This time let's figure out what we want psionics to be before we publish the edition, even if it isn't in the core books.