Yeah, I'm all about this right now, but what about these Difficulty Level Settings:
1. Story Mode = Backstab, High Ground, Barrel Throwing, and all the things we have now. Loaded Dice by default, more inspiration points by default, unlimited long rests, etc. Game doesn't change much from current state except maybe more inspiration points handed out like candy at Halloween for those who hate failing on dialogue rolls and inspiration can be used for combat too so players can gain extra help in combat. Also, maybe less enemies in various areas like the Necromancer Lair, Spider Lair, etc.
2. D&D 5e Mode = Actual 5e rules implemented. No backstab or higher ground, etc. Potions are Actions. No food during combat. True RNG. No loaded dice. Enemies have true 5e stats like accurate HP and AC. Disengage is an Action. I mean full blown D&D 5e experience. Game is harder because it is full blown rules with no cheese and nerf.
3. Dungeon Master Mode = Like 5e except even harder for those who are insanely good. This mode would be for people who truly know all the weaknesses of every enemy and they can exploit them really well. More enemies with more HP and AC and so forth.
Why would you remove highground ? What would be the point of taking a good position in your system ?
I'm all for a better balance and various difficulty level but what you ask is a complete other system with bonus actions that becomes actions depending your choice (UI ?), a useless verticality except to shove, specific creatures for every mode, an action to heal (maybe) 1HP,...
Being 100% faithfull to the rules is not necessary and as you described it, it looks boring to me.
The game has to be balanced first and it has to have strong foundations.
Tweaks could then increase/decrease the difficulty (i.e +1/+2/+3 for highground, +0/+1/+2 ennemie's AC, +0/+1/+2 to allied ST or such things, barrel weight 100%,70%,20%,...).
Even Pathfinder that has A LOT of options to customize your experience don't allow players to custom what is action and what is a bonus action (Don't know the EN words for Pathfinder but you get the idea).
What you ask looks completely unreasonnable and would require to balance the game differently for all difficulty.
