Most players don't want a good, solid long term server now. It's a shame but true.
From what I can see there are a few core fundamentals for player retention on mir servers. Given the game client itself will never be able to compete with modern titles, you have to focus on what can be done well..
- The community. When it comes to mir, player numbers are so important as they are a finite resource. The community doesn't necessarily need to be "good" in the sense of people helping each other etc, but some good rivalries and healthy conflict is great for a server. This is often ruined by poorly managed discord servers.
- Individuals progression. This is really hard to get right for everyone. Given the above (limited player pool) you really need to cater for as many people as possible. You can't please all of the people all of the time, but there really needs to be a carrot on a stick for as many players as possible. The next part of everyone's characters progress needs to feel within reach and achievable. You need people to stay logged in pushing for their next bit of progress as long as possible, and need people to wake up the next day thinking they 'need' to logon as the next objective is just in reach. Many ways to do this but rarely do I see a wide enough range of players catered for.
- PVP. Mir is essentially a pvp game. Some people might find some fun from purely pve and they need to be catered for, but getting pvp right is so important. There will always be balance and class complaints, but the biggest issue I see on most servers with pvp is how quick the fights end. Overpowered something, maybe stats, gear, class, spells - whatever.. It caters for the few that achieve such an advantage. To limit the pvp advantages and allow lesser players to realistically compete although still at a disadvantage would increase the playability of a server for the majority rather than the few.. The few need to realise they need the majority to enjoy their advantages too.
- Limit the leaders. We have seen enough times now that people will pay levellers, buy their gear, no life level, camp to the point of borderline exploit bosses etc. This ought to be rewarded, but perhaps to a lesser degree. Be it hard exp curves at higher levels, more rested exp bonuses, dynamic rare drop rates for individuals - lots of things can be done here if people want to implement them. Reality is most server owners are catering for the ones lining their pockets most frequently. Understandable, but not sustainable.
- RMT. By now we must have all accepted how rmt affects not just Mir but all games. Personally I would now accept it and probably just allow it. Let everyone benefit from either buying or selling rather than just the shady ones. Huge problem here is of course GM corruption. If a server owner can earn £1500~ by typing 1 line - lets be real, within the mir community it's likely going to happen. And here is the death of private Mir servers unfortunately.
There's not really an answer because a GM can give an illusion of transparency but will also be in a position to cover things up too. Mir doesn't work with bind on equip items or attempting to de value gold in any way. As sad as it is I can't see this one ever being addressed like other points can be - so although I might have the odd dabble on good looking servers that pop up, the community ruin them for themselves. The ones that insist on having the biggest advantages through RMT will almost inevitably corrupt the server owner(s) at some point. It's a weird one because they invest heavily in a way that actually cripples + de values what they are investing in. But there are a lot of people in this world with more money than sense.
Good luck to the next upcoming servers. I will probably have a dabble, and it will almost certainly be short lived as a result of one of the points above.