Hear me out but a friendly server with pony and minecraft maps would be lit AF.
But honestly, if I could offer a real suggestion, if I learned anything in xG it's that if you want to build a population on a server the server should be simple, Like one or two maps tops simple. Our trade servers are the Perfect example. Our most consistently populated servers over the course of the tf2 division by far, and for most of their lifespan they had a combined two maps, Clocktown and Goldenrod city. And when tgh almost died right before and while I was DM I was a big supporter of the controversial decision to go back to 24/7 clocktown to save the server, and it worked. Now tgh and poke trade are still our most consistently populated servers, and the map pools have grown. So if I had to give some advice, I'd say pick a really cool, expansive, interesting map with lots of things to do, that people are actually passionate about playing on, base a server around it, and work from there until you have an actually good server that people spend their whole day on.
Tl;dr: I've been here a long time, and we've done this throw some plugins on a server with no passion for the mode behind it and just hope population appears a bunch of times. It's only ever worked with ZF, and youtubers + good timing was the perfect storm.
We have a way better track record with starting simple and working outward than we do with throwing all our hopes on dreams at a server and hoping it sticks. Just stop the cycle it's kind of depressing.
As an example/suggestion, taking hyrule off of tgh and putting it on it's own server would draw more population than minimum 3/4 of the other ideas in this thread. You guys shouldn't be looking for modes, you should be looking for maps.
This rambled, sorry, I've just seen this exact thread with the exact level of fake urgency at least six times, it wears on the soul.