So, seeing the huge increase in private classic servers (the two largest with lows of ~100 players online and peaks of ~1500+ players online each, and both with ~4000 registered players each): there is undoubtedly a market for this type of server, specially among current players.
I believe Square Enix should take de opportunity that the current servers need merging and while merging the 6~7 least populated servers into 2, creating one or two new classic server for players to start from scratch.
One server could be Chains of Promatia rules, the other could be Wings Of Goddess.
Maybe something not as spartan as a true classic, a little faster XP gain than originally, but definitely not as ridiculously fast as it is now (which, again, is just way, way, too fast, XP gains should be at least half the current speed on retail servers).
They could even have trustes, but limit one or two turstes per player maximum when soloing. And two or tree trustes per party. That way the game is still more accessible, without killing the whole journey that is the leveling game (bast part of the game) and partying with other players at each stage. They could even find a way to somehow increase the level cap on such classic servers and implement lvl99 content without breaking everything else bellow it and messing with the core leveling experience. That would be basically be a selection of only the best parts of the game, a pick and choose.
I do believe more than half the current player base in the retail servers would be more than willing to create a new character on any new official server Square Enix releases, regardless of the rules (classic or not), just for the opportunity of starting anew on a new server and replicating the experience of being a new player along with everyone else at the same time all over again.
So, that's my humble opinion and what I generally would more than love to see somehow in the game's 20th anniversary.
As it is now, I believe even FFXIV takes more time to max out to the level cap, which is sad. There are even many speedruns of FFXI now a days and it takes less time to finish the game main campaign and cap the level of a job with trustes than many solo Final Fantasies... a few hours only.
Again, to me the best part of the FFXI experience is the journey, leveling up in parties, and group play along the way. Having max level in two or three jobs as a long term objective to attain. When that is gone, game loses much of it's magic, specially when it's all so easy, there isn't even the pride of accomplishment. A more middle grounded experience would be perfect, I truly believe, and better for the whole game experience of old and new players alike (something not as spartan as the original, but definitely not as lonely solo and fast as current retail server status).
Now, you may disagree, fine, but one simply can't deny there is a large public for said type of experience (from famous youtubers and twitch streamers). Many players whom don't even participate in forums or reddit (most players, actually) would get behind such an idea. On private servers alone one could amount ~ two thousand players that would love to play in an official classic server.
So many new and returning new players lately, by the hundreds, many would love to relieve that original experience somehow (eased a little bit, yes, but not completely dumbed down and streamlined as it currently is on retail servers). Also, most players I know usually stop playing any MMO soon after reaching max level and finishing most of it's "story" content, that is the true for this type of game and probably true for most new players incoming.
Thank you for your time and attention (even you disagree) : )