I think there's definitely a learning curve involved with a player who wishes to switch from a trans class server to a third-class server. There are new skills and the renewal mechanics to get used to.
I agree with the suggestion, but honestly speaking, I'm not very moved or motivated to try the third classes. I don't spend a significant amount of time playing Ragnarok Online. I don't like hunting for gears, so I never farmed or hunted for anything here. I don't like leveling new characters. I don't like trying new builds.
So honestly, I'm more like, "Gee, let's do some PVP for a little bit" and log off. I don't really have the chance to become bored with ForsakenRO, so I'm really okay with staying as a server without third classes.
The idea of a test server is a good one as it will really let key players give an input of whats balanced and what is overpowered so we can have a solid foundation of where to begin with a potential transition. With this in mind, I wouldn't expect to just see an official third class update in like two to four months as I feel like this is a really sensitive matter in which it should not be rushed by any means. I'm not saying the team would be slow at rolling something like this out, but the testing players should really and really play with third classes for a longer duration to accurately measure their comfort or discomfort involved with the introduction.
This mix of players should include people who want to see third classes, people who are extremely against it, people who have never played third classes, and people who have played third classes on a another server so they have kind of a control group in which to compare against.
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And honestly speaking, if the current equipment that players own cannot be moved over to a renewal switch, I would be extremely against it. I donated for everything on my characters and I mean everything. Even if I hunted for everything, I wouldn't want to spend more time re-acquiring equipment, as I'd rather devote my time to getting used to new battle mechanics and new skills.