Personnally I would want Mongoose to avoid the Überalf-syndrom in which TSR fall. If elves can be portrayed as CG free-spirited sylvan people rather than LE supremacists who are intrinsically better at everything than everyone else, period; that would really be a breeze of fresh air. So, not something like the Complete Handbook of Elves or any 2e FR book with background on elves. People who love magic, but are not themselves magic. Who live much in harmony with nature, but are not fey. Who are skilled at some craftworks -- especially of wood -- but not the best artisans creating artifacts each time they hammer a nail into a plank. Elves from the D&D Monster Manual rather than from the Silmarillion (a nice book, but an universe totally unbalanced for a RPG !). It's this growth of power of Elves that make me dislike them so much.