That's interesting. I feel like I'm somewhere in the middle. I think, on shows like the X-Files, they need to have some sort of "rules" - on Supernatural, I believe they have some semblance of rules - essentially that there are no rules. Heaven and Hell exist. Other gods exist. Fairy tales exist. Magic exists. All the fables and stories are true. Our world is real. Scooby Doo is real.
At the same time, I feel like aliens are too far on Supernatural. If aliens showed up, I feel like that would be weird. It wouldn't be a dealbreaker for me, but I feel like it'd be weird.
I do feel like the X-Files liked to tow that line. Simply having Scully on the show implied that there needed to be a scientific explanation for everything, but they also liked to challenge her with things that she couldn't explain. Same with Fringe. It's a realistic, technobabble X-Files, but they liked to push the boundaries of the explainable there.
With Sliders, I think the rules sorta get thrown out because "anything is possible." Even with Quinn or Arturo occasionally playing Scully, they didn't really try to understand how there could be a universe where the rules of physics don't really apply. As if there's some sort of branching possibility with physics being "created."
For me, I know what I would do. It's what I did for Earth 214 (I think), and it's what I've suggested to a lot of people who've asked me about fanfics - and that's "try to think through each world." The most fun part for me about writing Sliders is trying to put real thought into each world you come up with. If you want to write a story about the French ruling America, come up with how it would work and follow through. Maybe Napoleon was never defeated. Then what. Then what. And I'd try to have something in the episode that shows that we did the research and put thought into it.
Where this gets me into trouble with most people is that doubles probably shouldn't exist. This definitely came up after E214, but if I were doing Sliders, doubles would either be very rare or completely absent. Fraternal doubles should exist, but if we're talking about a world that separated in 1776, it's very unlikely that every human that was born from 1776 on looked exactly the same. And if one person looks different, then every subsequent birth should be different. If Quinn's grandparents look different from Earth Prime to British Earth, then Quinn's parents would look different and then Quinn would look different. And that's if Quinn's parents ever meet in the first place.
If you want doubles, you sorta have to write into the rules that "certain people are supposed to exist the way they are." So there's some sort of predestination where Quinn always looks like Jerry O'Connell. But then you can't play around with Robert Floyd as Quinn or Logan St. Claire. Because if the universe always makes Michael's sperm and Amanda's egg magically meet to create Quinn, then you have to stick to that.
And hell, if you want to get really deep into the deep end, there's the idea that human beings are unlikely. Life was unlikely. If you actually looked at infinite Earths, I'd think the vast majority of them wouldn't have life at all. And then there'd be a vast majority of Earths with life that doesn't look anything like the life we know. Language would vary from Earth to Earth dramatically. In that case, Sliders would resemble Star Trek more than Sliders.
To explain this, someone here had a great analogy. Think of sliding as a vehicle in a town. Every house is a different parallel Earth. You can very easily travel from house to house, and the people in every house might look different but they'd typically have a lot in common. They'd speak the same language. Go to the same schools. Shop at the same stores. One family would be pretty recognizable to another one. You'd need a more powerful timer to go to a different part of the city. It's still be recognizable - the people would still be citizens of the same town but the kids would go to a different school, the people might work somewhere else. They'll shop somewhere else.
You'd need a more powerful timer to get to a different part of the state/region/country. A lot of things would be different but still very recognizable. But the further you get, the bigger the differences would be. Dialect. Language. Nationalities. Ethnicities. Politics.
The "rules" you establish could simply be that Quinn's timer is a scooter. It can go from house to house, and with enough work, it might be able to get around a city. The city is a place where Humans are dominant, the languages are recognizable (not always English but always an Earth Prime language), and history is familiar enough. The worlds where life evolved into something unrecognizable, where language isn't decipherable, where the air isn't breathable, where the worlds are more alien than anything....aren't accessible to Quinn. Maybe they aren't accessible to any Slider.
That's how I'd make it work.