James Gasik
We don't talk about Pun-Pun
Any DM who encounters a rule they don't like can change it. That's as true today as it was back in the 70's. If there's a DM outside of public play who doesn't have their own list of house rules, I'd be very surprised.I'm glad for that, personally. In practice, "rulings, not rules" often means that individual DMs have to spend time making up common things that ideally should already be in the books they've spent sizeable chunks of money on. I like homebrewing, but 5E leaves the DM to do the heavy lifting way more often than it should IMO.
We don't need to write a rulebook with gaps to facilitate DM's into putting on their designer hats- each group has it's own needs, and if the rules don't serve those needs, they can be altered. This isn't the Hackmaster-verse where you need to pay dues to an organization to play the game, which has bylaws and enforcement, thank (insert a Power or Powers you may put your faith in here)!
What we do need, is good advice for recognizing when a rule isn't working out for our group, and how to deal with it. When I was a less experienced DM, my attempts to change rules always fell flat because I failed to account for the fact that rules aren't isolated entities- they exist in a rules system, and many rules rely on others to function.
That's an important distinction and the main reason why you can't have shoddy, open to interpretation rules laying around, because that makes the rules that interact with them equally open to interpretation, and pretty soon you don't have a game that really functions on it's own.
It's like a Bethesda release (Skyrim is the ur-example, but there are many others)- you install it and find it's buggy and somewhat lacking. Sure, you can go to Nexus Mods and load up on bug fixes and custom add-ons to your heart's content, from making the UI friendlier, to making all the women hot scantily clad babes to making the survival elements more pronounced, to replacing all dragons with The Macho Man Randy Savage if you want to- but if you have to put all that work into making a game good...how good is it, really?
It's the Ship of Theseus problem- how much can you change 5e and still have it be recognizably "D&D"? From very early on, the 1e DMG told me I could totally have adventures set in a post-apocalyptic future, the old west, or outer space (Sci Fi outer space, not Spelljammer).
Now D&D's rules systems might not be the best fit for this sort of thing, which is why many, many, many other games have spawned over the decades, but people who love D&D love modding the hell out of it, and that's a good thing- absolutely, you should do this, and I encourage you to do so!
But you don't need a bare-bones, awkwardly-worded system to facilitate such endeavors. I think a consistent system where the designers are open to explaining why the rules are the way they are, what thought processes were going on, would be the best possible starting point. If you know the assumptions, you know if those assumptions work for you.
For example, take the eternal hand wringing debate about survival exploration in D&D. The evidence shows us that with generous carrying capacity, goodberry, tiny hut, Outlander backgrounds, create food and water, purify food and drink, bags of holding, etc. etc., that the people who make the game don't think this is a serious concern and that any group should be able to nope out of it.
But then they consistently tell us that "exploration is a fundamental pillar of D&D, and we want to support it" without actually doing much more than lip service towards doing so- and when they do take steps, the instant they receive any negative feedback, they scurry back to their ivory tower and say "see? nobody wants it!".
It would be much more preferable, IMO, if the DMG section on exploration said something along these lines: "Most of us here at WotC don't care for low fantasy play where players have to carefully eke out an existence in a harsh, unforgiving land. And there are a lot of people who agree with this standpoint. So by default, our product does not support this sort of play. However, if you want this in your games, here are some suggestions, and possible pitfalls you may encounter."