This quote answers some of the questions raised:
"Oversight was created as a stop-gap, to deal with the high-priority
cases for high-level revision removal due to privacy issues. If
revision deletion bitfields go into full use later, there won't be a
compatibility problem; we'll just stop using the old oversight
system."
-- Brion, December 2006,
http://www.mediawiki.org/wiki/Talk:Bitfields_for_rev_deleted
--
Yours cordially,
Jesse Martin (Pathoschild)