Sorry for late reply, but wanted to add my impressions.
I personally still do think that vanilla pre-re is the best setup Ragnarok Online had. It had this unique feel of you exploring the vast world without anyone telling you what to do or where to go. You could just be like "Hey, let's do a Glastheim party today", run around Prontera and ask people to join you and it actually worked.
This made RO so special for me compared to all other MMORPGs where you just follow a linear line of endless quests and nobody ever joins you party out of instances because "sorry I'm doing a different quest".
And people are fairly vocal about missing the Ragnarok Online how it used to be. And yeah they aren't just a vocal minority, there are actually plenty people thinking this.
So why doesn't it work out?
First of all, let's look at these people. They are all veterans, probably 95% of them all played official RO before the renewal update at some point. Being veterans, they've seen everything already, they have mastered the game, know how to break it. You cannot party with them, because they have mastered the art of multi-clienting so well they can level up much faster playing 2-4 characters at once. Pretty much all priests on the server are just made as buff slaves rather than main characters. Without a priest, no good party.
So even if a pre-re vanilla server with a great admin opens up, the playerbase itself is already making it impossible to re-live the good old times.
For that to work, we would need new players, which is the second issue. Imagine you're a new player. You heard about Ragnarok Online from a friend or because you requested an MMORPG and got suggested that. If you're lucky, people might even have suggested you to check out private servers because the official ones lag and are full of bots. What are you doing? Well you certainly never heard about emulators or RMS. So you just google for "Ragnarok Online best private server" or something. And what you get as result are these strange toplist sites. The top entry is usually a high rate server, because HRs are simply the most popular due to many people just wanting to do WoE and not care about leveling. Now, you might already figure a high rate ruins your experience as new player (but most people will probably not figure that), so instead you pick the first low rate server you find, which is TalonRO. You can read what customization TalonRO has, but as a new players those lists are completely meaningless to you as you don't know what's good and what's bad. If anything you as a new player would think that "the more updated the better" and refrain from going to a pre-re server because you see other server being on a higher episode.
In short, new players either end up on official servers, a high rate server, a renewal server or TalonRO (which is not vanilla at all). A new player wouldn't even know how great it can feel to not have customizations or low rates. And after being spoiled by customizations and high rates, it's usually impossible to come back to vanilla, if you had never experienced it before. So the people who could potentially re-live all the great feelings we had when we first played RO and consequently also form parties are just not there.
The third issue is that the veterans on pre-re low rate servers are to a large portion pure WoE player that only don't play on high rate or instant WoE servers because they consider grinding and gearing up to be part of the WoE challenge. They don't care much about having fun partying up at all. That isn't bad in itself, but the problem is that WoE players are not too loyal to a server. Once all guilds are geared up, usually one guild crystalizes as being the strongest and eventually WoE stagnates because always the same guild wins. The other guilds leave for a new low rate pre-re server where they can gear up fresh again. That was the situation of pre-re low rate vanilla servers from like 2009 to 2016. And you know what happened to the PVM player of those servers? They stuck with the server until it died, then moved to the next whenever a promising one came up and then eventually they grew tired of server hopping and said "Screw it, I'm going to TalonRO, at least that one doesn't close after 3 months". You can bet that by now the remaining players that actually would like to play vanilla pre-re RO and haven't quit RO yet are actually on TalonRO despite its customizations. Because a stable server and large populations in the end beats the wish for reliving the good old vanilla times.
There might still be a thousand people around that would love to play vanilla pre-re RO again, but they are all tired of server hopping and veteran players who only care about min-maxing and have given up on ever experience it again.
And there might be thousands of people who never played an MMORPG before and would love pre-re vanilla RO if it's their first MMORPG experience, but they will never even end up there.
