The population of Low Rate servers is always the same one, which goes back and forth between servers everytime drama or hype occurs, that's what I've noticed.
However, those servers really differ from each other. If we take retRO vs OathRO for example, the latter basically rewrote entire skills, while the other one tries to keep the game as you always knew it - with episodic changes. Honestly I don't know where their source is, I kinda remember some changes (Summon Flora summoning Parasites before ep 9 for example), but other than that the game is still the same. That's the RO we all love. The server feels empty though, especially on european time. Most of the players now are americans, parties go on most of the time though, either magma or niff. There's always someone in Louyang. Prontera is not as busy as a few months ago, but shops are there and the occasional chats between players in south kafra make the server look alive - barely.
As much as I would love for the servers to merge, when it comes to low rates it simply is not possible. This game is a grindfest in which you have to sink hundreds if not thousands of hours to build your characters. I play in retRO, and I'm not quitting after the work I've done, even if that means playing with just a handful of players or during woe time. I spent too much and I'm attached to what I have. Me personally, I don't see myself simply quitting and start over on Oath, Origins, Travels, Koko etc.
I like what the staff is doing in retRO (even though they REALLY should advertise it more). There were some hiccups to be fair. Exp x2 event way too early March last year when the server was 3 months old and never to be seen again; majoruros exploit and a few guilds in WoE smashing the competition; were just a few of the things that made people leave this server in favor of trying another. I play mostly solo, I enjoy WoE on this server and whenever there's a party I try to attend. Community is tightknit, because the server is small. I am enjoying the episodical content and the game is how I remember it. I simply wish more people could come and try. It was fun when the server had an average of 100 players not counting autotraders.
But I know it's the same for other servers, too. Once you start a low rate, it's difficult for you to simply quit and restart. Regarding your topic, you can't simply merge low rate servers, because the developers of these servers rightfully have different visions.
I think we should learn that servers now (low rates, at least) will never have the population of officials with official mechanics. You have to choose one of those things, and decide where to stay accordingly. This is just my 0.02
