Proposals aren't the law. Opinions aren't the law. You have to go with the law as it stands. Part M as it stands will be the law as of 28-9-08.
An EASA Opinion is essentially a draft of legislation sent to the European Commission. The Commission, or the Council of Ministers, or the European Parliament could reject it, but at this stage that seems unlikely, so I'd say it's wise to plan for it being 'the law'.