In short, I believe people should still contribute where they see they can add
the most value and according to their time schedules. Additionally, others who
have more time or the ability to refactor for reusability should be free to do
so as well.

I agree that people should be able to contribute where they can; at the same
time as a single unified project (lucene+solr) I think there is an objective
'right' place for things -- code designed to have maximum utility and reusablity
(minimum dependencies without sacrificing functionality).

Starting things in the right place is often easier then refactoring later --
that said, i don't think it should be a requirement as long as we all agree that
things can (and should) be moved to a more reusable place if someone is willing
to do the work.

Thinking about the issue that triggered this debate... in SOLR-2272 (the
pseudo-join stuff), I think the heart of the problem was the idea that once
committed, this new feature could not be moved around. With this discussion, I
think we agree that it should be refactored if someone is willing to do the
work. It may even be reasonable for someone to mark it as @lucene.experimental
if there is serious concern about how hard it is to refactor (and that person is
planning to put in some effort to move things in the right direction)