Really, tweaking any skill's behaviour requires extremely minimal effort. The same goes for items, and yes -- even tweaks to model animations (from 1.5xx it should even be as simple as just replacing the couple of required model/animation files, as they should still be the same format. Manually tweaking is also fairly simple though; there's working editors for that).
Kallop points out that he doesn't like new content, he prefers older content. Regarding the game events, does it really matter if there's additional events you don't personally wish to participate in? Unless I'm not aware of something (which, honestly, I probably am), the older game events really haven't changed all that much; the biggest change I can think of was to make use of newer client functionality to capture monuments and such properly instead of having to kill/destroy them (and I'm not even sure that's available in the 1.8xx client, but you know what I mean).
He also points out that he prefers the older maps; sure, that's fair enough. Everyone has different likes/dislikes. Some people will prefer the older maps, just as others will prefer the newer maps.
Probably the best thing to do here is put it to a community vote to decide which they'd like to use, and possibly change it around every so often (even if they're just brief changes), just to spice things up.
Skill effects are trickier. They're essentially drag & drop, but again -- everyone has different likes/dislikes. I don't see any reason the skill effects couldn't be interchangeable; private servers have, in the past, offered UIs, item icons, and even skill effects for those who prefer them.
I get that if you're dead-set on 15xx functionality, why bother with 18xx. If you're not going going to use it, there's no point in it being there. Additionally, why bother tweaking skills to suit if you preferred how skills already worked in 15xx.
I get that, it makes sense, and there's nothing wrong with that.
Having said that, at the end of the day, I don't particularly think it should matter if it's a 18xx client/server with 15xx functionality. There should be very little noticeable difference for players.
I mean, sure -- the UIs are different, but if that bothers people so much, revert them. There's 1.298 servers using ROFD and newer UIs, so this is nothing new. As previously mentioned, you could just provide drop-in replacements, servers have been doing this already.
There's new (or modified) skills -- but there doesn't have to be, they can just as easily be removed, tweaked, or even simply completely replaced (being the fastest/easiest option). TBL differences are extremely minor, so you should just be able to replace them outright and delete a few columns for consistency.
New items -- so don't make them accessible in-game. Purely database-related and extremely trivial; if you don't already use them, then you don't even have to do anything; there's not really much reason to do anything with items.
New zones -- also trivial. Just replace the map files. This is even easier than trying to make it work with older clients like 1.298/1.310, as the format's not even any different between the two.
New skill effects -- as above, format's the same, just replace them. People have been doing this since 1.098 times.
It may seem like the above is a time consuming process, but it really isn't -- it should take well under half an hour to do so (the majority of which, I attribute to the awkward layout of skill effects).
Understandably, you're probably still thinking "but why bother with any of that when you can just use the 15xx client?" -- and you're not wrong. If you really, really, want to use all that stuff as it is, and don't plan on doing much if any custom work, then there's probably not much point in tweaking the newer client at all. All, I suppose, you'd really get out of it it would be the various client bugs that were fixed since.
I'm honestly not sure where this confusion came from, especially with the current state of PSKO being all over the place with its various 1.298/1.310 servers trying to mimic all sorts of official versions as best they can.
Players shouldn't associate client/server versions with official, for one simple reason: you can always provide backwards compatibility. As explained above, changes are fairly trivial.
The one thing to understand about KO is that it really doesn't change. The looks may change, they may add an event once in a while, some items, or even some skills, but the client, nor even the server really changes aside from making way for any actual new functionality (which is far and few between).
This is why I'm a little confused as to why this particular server decided to give up and jump ship back to 15xx. So far there's only one 'real' (i.e. not just the preference of zones/skill effects, but something that directly affects gameplay) problem that's been mentioned, and that's the added cooldown to minor heals, an extremely minor (pun not intended) issue that requires tweaking one value in the client & server (really, that's it).
I'm genuinely curious at this point as to what people really have an issue with; visual preferences aside, why the strong dislike?
The other item briefly brought up was "balance issues", but this wasn't elaborated on. Balancing issues with what?
I personally prefer to work with the latest as it offers a great deal more potential for customisation. For instance: the ability to actually capture monuments properly is a nice touch, and far better suited for those events than their hacky "kill it to cap it" workaround. Additionally, things like item manufacturing don't need to work as they do officially: you can throw in your own recipes, and do whatever the heck you like with it. It's a much nicer solution than being forced to use quest NPCs to achieve similar functionality (admittedly, both fairly trivial examples, but you get where I'm going with this -- I hope.).
However, if there's such strong dislike to these newer versions (and here, I'm -- as Kallop mentioned -- referring to behaviour as it is by default, in official), I'd really appreciate the reasoning behind it. As most if not all of you know... I don't play KO, so I rely almost exclusively on community feedback for learning about things like this, that could only really be experienced by properly playing the game. So thanks!
Man, this thread's a little derailed... oops!