In My Experience... (Score 5, Interesting)

I don't think that the developer of these games really needs to plan something special for the long-term players as long as they make all your achivements scalible.

Now I have never played Lineage myself but from what I've read about it this is a good example of game that has such a scale. Once you have gotten a strong character you still have other things too look forward to, mostly Guilds. Once you have found a guild you can build your guild and capture castles.

Now these high up players may eventually own one of these castles but this still gives them many things to do; for example they must defend their castle, they must manage it, and perhaps they eventually get bored with this and go to capture a second castle?

Games should not have a definete ending for the players. The best online games I've seen are the ones that let the players fight against each other and put in balances so that no one power can ever overwhelm another.