Heedless of the initial RFC <http://www.nntp.perl.org/group/perl.datetime/2009/04/msg7245.html>, I have forged ahead with DateTime::Span::Common <http://search.cpan.org/~tbone/DateTime-Span-Common-0.01/lib/DateTime/Span/Common.pm> and will be reaping the benefits of it in my codebase shortly :)
http://code.google.com/p/cpan-modules/source/browse/datetime-span-common/DateTime-Span-Common/lib/DateTime/Span/Common.pm