I am concerned that the current handling of copyright problems on
wikipedia may be insufficient. As it stands, after detection the
offending text is completely removed.
Unfortunately, if there has been a long time span since the insertion
of the infringing text there may have been a substantial number of
valuable contributions to the article. With the way that most content
grows organically over time, it may be very difficult to say if the
new text would have been created without the infringing text with any
certainty.
In the United States the recent tendency in court appears to be to
favor the most expansive definition of a derived work possible.
Because of this, I suspect that it would be likely that at least some
of the contributions made to an article after the insertion of
infringing text would be found by a US court to be derived, thus
placing their ownership in question. This interpretation of derived
isn't necessitated by current international treaty, and would likely
be different (and possibly more sane) in other locations, but I
suspect that US legality is a substantial concern.
Determining if a piece of text is derived from another, at least in
the over broad sense favored by US courts, is an intractable problem,
but the policy could do a better job of avoiding these concerns.
Reverting to the point where a substantial amount of infringing text
was added, and deleting *all* modifications after that point would be
much more certain to avoid impinging on the intellectual property
rights of others.
The cost of destroyed improvements might be mitigated by the benefit
of creating a greater incentive for frequently contributors to quickly
catch and remove violating text.
Of course, none of this is legal advice...