Speaking as a millennial (and someone who was initially drawn into ponies by fanmade G4 content and memes), it would very much depend on the show.
FiM was one of the first in a big resurgence of high-quality cartoons alongside shows like Adventure Time and Gravity Falls, which appealed to both kids and those in my age group who grew up in the 90s/early 2000s during the 'Golden Era' of cartoons (and that's not just my nostalgia goggles talking, it actually is called that in animations circles
). I think a lot of fan content was a perfect combination between millennials getting to an age where we had the time, skills and energy to make ambitious content like fanmade episodes and tons of fanart, and the appeal to our childhoods with Golden Age cartoons.
The next gen cartoon (not sure if Pony Life stuff counts as G5?) would probably need to be in the same kind of vein, with a good overarching plot and worldbuilding, decent animation/visuals, good characters, and also be lighthearted enough to offer an escape from everyday life. Although 10 years later and following on the heels of things like Steven Universe, the bar might be higher now than it was when FiM really took off. It would also have to appeal to those who are currently teenagers since they're likely to be a major force for content creation today - but I think their cartoon tastes do overlap with millennials, seeing as they literally grew up with AT and SU.
I think it's plausible, but the people who make the next show would need to be ambitious and committed to making a good cartoon and not exclusively see it as a vehicle for selling toys. Most of the 'good' cartoons with lots of fan content these days are made by people who genuinely love making a show and bringing their creation to life, which really shows and is much more appreciated by fans.
I just hope the next show wouldn't also draw in a large and... less savory crowd. I genuinely think FiM had a huge problem with that, and it's part of the reason I and many other people fell off the FiM bandwagon.