It would be great if we had a couple of extra collection filtering/mapping method out of the box. It looks like overriding \lithium\util\Collection in a project would be quite complicated (I don't really see how to do it easily).
I'm thinking about ECMAScript5 functions like filter, any / some, include / contains, all / every : you can check them at : http://underscorejs.org/#collections
any / some
include / contains
all / every