I think we we're promised that XP would not be wiped.
Given that that is the case, please try to find a way to keep your promise. Other people have made suggestions and perhaps you could ask for others in case there is a better solution to the problem you percieve.
If you think that it will give us a unfair advantage, I understand, but I believe a consequence will be that some experienced players will prey on new players to recoup their "losses", real of imagined. This may lead to some very, very bad reviews.
One idea, if you sink a player several ranks below you, you lose XP and so possibly lose rank. This might deter old hands from sinking large numbers of new players. This may be unworkable, but breaking your promise about XP is unpalatable.
Kind regards.