As a long time play tester of table top games from WotC, White Wolf and Catalyst I do have experience in "testing and balancing out dozens of different combinations of options."
I do understand where you are coming from. The great thing about the 5e system for D&D is incredibly simple and what I'm proposing isn't unreasonable. I'm not asking that they go through the entire Unearthed Arcana and add every variant rule. You chose to quote my TL;DR that had no reference to the examples I suggested and those were all things that are already in the game that can be change or isolated to a toggle as well as things that are already present in Larian's previous game.
As for Balance. I understand that the things I mentioned weren't all inclusive, however; what I mentioned wouldn't impact balance of the main game because the main game and the standard difficulties would be the vision of the game Larian already has in mind. The custom things that can be change can/will/should break or impact balance; that is the whole point. If you are customizing things you are doing it with intent and it's way more about player experience rather than balance at that point.
Take for example: D:OS2 they even have modes that does just that; broke balance intentionally.
![[Linked Image]](https://i.imgur.com/aP2aDKX.png)
An example form Baldur's Gate: Enhanced edition
![[Linked Image]](https://i.imgur.com/PsON7DO.jpg)
An example form Icewind Dale: Enhanced edition
![[Linked Image]](https://i.imgur.com/ynrRVvb.jpg)