This idea is very raw still and lacks a lot of details, so i'm sorry for that. I ask community not to response with simple "it's terrible" without any further explanation.
For now at some point of world's evolution many players feel a lack of motivation for further character development, if they are not a part of main factions and are not involved in eternal wars. You may call them "casuals" or "wimps", but in fact when they loose their villages, characters and stuff, many of them just stop playing and start to wait for another world. Some others feel that current world is just "too much flooded" with players presence and wait for "new clean world" too. Since there's no progress transition between worlds, people feel no need to start playing over at the "world's end".
My idea is to create some kind of "global account progress": when character will die (by act of murder or due to the world end) it's skill points score will be added to it's eternal spirit's score pool. These spirits live in separated "spirits realm" (or "Valhalla" if you like), where player may log in as a spirit any time and spend these points for some "fun stuff" - change spirit's appearance to more complex, create some environment objects or "gear" for the spirit, interact with other spirits.
This "spirit's progress" should make no or minor "cosmetic" impact on next player's incarnations in physical world, but will remain in the realm of spirits.
Sorry for my EngRish as always and thanks for your attention.