The obvious steps to me are to make minor modifications because no one knows what went into the secret sauce of making 5E as popular as it is.
Maybe not with complete certainty, but I think we can make educated theories.
Start with the fact that its popularity is largely due to the large number--a majority--of new fans it brought in. Sure, lots of folks came back-whether people who had moved from 4E to Pathfinder, OSR games, etc, or folks that had just stopped playing--but we're not just talking about a renaissance, but an explosion of popularity. Meaning, if it was just us old-timers dusting off our dice, then we'd be talking about something closer to the 3E revival, or maybe a bit more. But we're talking about a new player base that is multiple times larger than that.
If it
was just a renaissance, then we could focus on the game itself and what it does well (or well enough) to win people back to playing. We could look at its "classic" vibe that harkens back more to 3E and before than 4E. We could even focus on specific elements like Bounded Accuracy. And perhaps most especially, the more temperate release schedule (which is probably the single biggest internal factor).
But because the immense popularity is largely due to the influx of new players--Zennials, mainly--then it probably has more to do with outside influences.
Stranger Things could be the single largest contributing factor; I don't know the number of viewers, but it is probably high tens of millions, if not 100 million+. Then you have a confluence of other factors, some specific, some more nebulous: Critical Role and quasi-celebrity players, the popularity of comic book movies and the mainstreaming of geek culture, accessibility and the convenience of gaming apps, as well as online gaming and lockdowns, and perhaps a kind of general digital ennui that leads young people wanting more organic, imaginative experiences.
So I think we're on solid ground if we posit that 5E is as popular as it is because of a perfect storm of cultural factors, most especially
Stranger Things. Sort of like a soup: Lots of ingredients, but the "star of the show" (the meat, if you will) is Stranger Things. But lots of other ingredients, with a "broth" of a general cultural moment. And because of that, it is less so about the game itself--whether the mechanics or presentation--and more about external factors. The game itself probably helped
sustain popularity, but it didn't create it. To use another metaphor, it is like a rising wave that WotC was able to successfully surf on, both because of a good surfboard (the game mechanics) and skillful surfing (marketing, release schedule, etc).