Zardnaar
Legend
Obviously, like the diversity of boardgames, there can be a be a diversity of roleplay designs.
If the goal is to reach the widest audience possible, probably it is wisest to use 5e as the starting point. It did and still does represent the emerging consensus of D&D players. For 2014, the ones who filled out the surveys were mostly grognards from earlier editions. Now for 2024 5e is pretty much the only D&D most players have known during their lifetimes, if they started playing around the age of 10.
Even Odyssey seems to use 5e as its chassis. Its levels 1 thru 10 correspond to 5e. Probably, one can pull a monster from the 2024 Monster Manual and play it as-is for an Odyssey campaign, and viceversa. If the Odyssey Magic-User class was a new "prestige class" with only ten levels, I suspect one can play it as-is in a 5e campaign.
5e design is remarkably robust. It can tolerate much modification and still seem to carry on. Tweak it to taste. Each setting can make 5e its own.
In my homebrew I replaced 4E engine with 5E. Reason was everyone knew the 5E engine and you can tweak it to Fort/Ref/Will for example. Reverse OSR saves everything is DC 20 add your save modifier.
You could make a more evolved B/X, 3E,4E, new edition etc.