You're missing the point. The 2014 options worked because WE (the DMs) knew how to make them work. For example, there is an option to make short rests 5 minutes and long rests an hour. It's called epic heroism and it's given two whole paragraphs in the DMG. The only suggestion it gives is couched in "you may want to" and that's still "slow down spell slot recovery and consider using harder fights".
Now, you and I know that making rests that easy means PCs will chew through material much above their level, the encounter guidelines are useless, treasure needs to be reduced to compensate, and there is absolutely no way you can run any adventure as written. We know this because we are familiar with the general balance of D&D and 5e in particular. But what does a new DM (or one who doesn't dive into the metrics of the game, there are DMs who don't care about such things) do when they see that, think "yeah, that sounds cool" and implement it for their next campaign? Disaster. And WotC doesn't explain why you have to do more than add an extra few monsters to the fights.
For such a system to work, a lot of things need to be accounted for. The recovery rate of spell slots, character features tied to SR/LR. Magic items. Encounter building. Adventure design. Things that take more than two paragraphs to explain. And that is one example. What if I combine Epic Heroism with Spell Points? What are the perils of that?
So maybe it's better to take things that easily break the game and remove them for the core books. Put them in a supplement where they belong (be it an official or a 3pp one) where the ramifications can be spelled out in more than two paragraphs.