I seriously doubt that this would happen. M$ would have to buy out Macromedia and I don't think a merger is likely to happen. Flash is too important to Macromedia for them to just let it go.
On the other hand, a collaboration between Apple, Sun and Adobe would be nice to see. An open source format to compete directly with both Flash and Shockwave. For one thing, the Flash Communication Server and Flash Remote Server aren't available for Mac, and will probably never be. Both products are WAY too expensive and somewhat limiting. An open source competitor, if done correctly, would destroy Macromedia.
Another thing about Macromedia is that they seem to be pro-M$ and anti-Apple. I'm tired of seeing .NET all over their products.