My PHB rewrite to both make the game feel more like AD&D and fit my campaign better is well underway. 123 pages. Lots of modifications to make it more "realistic" and more gritty. For eventual DMsGuild publication.
Level and spell level limits based on abilities.
Class and race restrictions also based on abilities.
Modifications to every class, and it only covers the core races and classes in my FR campaign that started AD&D -dwarves, elves, half-elves, halflings, and humans. Gnomes might be added but they never played much of a role in my campaigns. Classes are bard (completely reworked), cleric, fighter, ranger, paladin, wizard, and a new sorcerer, with a new magic system just for them.
Other classes - druids, warlocks, etc. will be NPC only for now (and not in this book)
Traits, feats, and other customizations have been altered.
Equipment changes cover specific purposes for given weapons. Armor has a higher AC and provides resistance to one or more damage types. Certain weapons are worse against certain armors - a rapier against plate for example, and others are designed to overcome these - an estoc is designed specifically to pierce plate, bodkin arrowheads are better against plate than padded (textile armors), broadheads are better against padded than plate, etc.
Exploration and adventuring includes more coverage of traveling, hazards, resting and sleeping (quite different), aging, and more.
Combat is based on using your combat modifiers (DEX and STR) as either to-hit bonuses, or AC bonuses on a round-by-round basis. You can choose to directly parry an attack, including as a reaction, and combat fatigue is a thing. Called shots, tactics, grappling and combat maneuvers, and control of the battlefield (but no battle mats) make combat more closely resemble real battle tactics, rather than tactics based on game rules. Fighting defensively, learning your opponent's strengths and weaknesses, and finding ways to gain advantage, etc. Yet it's still very fast to run, and uses existing mechanics.
Spellcasting has rules for research and learning spells, casting spells you haven't mastered yet, a number of different potential points of spell failure and expanded Wild Magic Surge rules to support them.
Conditions include many that leverage the exhaustion track and death saving throw mechanics. Debilitation (pain), injuries (that can last days or weeks), ability damage and other similar effects that make sense, and put the fear of poisonous and undead creatures in particular back in the game. Healing magic is also altered to address these changes, diseases and injuries for example are much harder to heal.
I also have magic item creation rules, although they probably won't be in this book. Like the other rules, they are written with consideration for in-world ramifications, rather than making it easy for PCs.
I could use some help with artwork, and also with proofing/playtesting.