There is absolutely no reason to believe that Flash 10 will ever be available as part of the official system. Adobe wants licensing for (mobile) Flash 10 that Nokia understandably doesn't want to pay (again) for the N900.
Can I license Flash Player for distribution on mobile devices? Members of the Open Screen Project are able to distribute Flash Player 10.1 with their devices royalty free; however, a license (contract) still needs to be in place between Adobe and the licensee.