Okay...Here's my two cents. I think some of the worlds are in a bad way and merging would be the fairest option. (Simple removal would rather be a negative for many players.)
If a player has character in both worlds, assuming character merger is not possible, I'd say compensation would be in order for the time and effort lost. If possible, I'd say the player should have a choice at login after the merge to pick the character to keep vs lose. I have heard nuggets recommended by others, and I am inclined to agree with that. (Perhaps a formula to account for level, items, coins and gold in the account?)
I like the idea of managed worlds like W6 personally. I also like the named rather than the numbered worlds, so if we do go with mergers, I would strongly suggest the worlds end up having names rather than numbers since it gives them more personality (at least I think).
Anywho, looks like I gave my two cents and tossed in an extra half penny.