de-open source - Oracle/MySQL

Reasons for moving from closed source to open source could be for

1. Company wanting to benefit from community contribution in terms of
   code addition, code modification, code review & product testing
2. Company folding - so, open source the product
3. Older product or version of product
4. Company getting good will
5. Opening more usage of the product

Recently, I am suspecting some companies could take their code closed source - from open source. I am suspecting dual license can enable this to happen.

My fear is MySQL, used by many companies in production, going closed source. One theory (or did I read somewhere?), was that Oracle purchasing Sun was for MySQL. If it had purchased, MySQL directly, people could call foul easily.

Facebook is using MySQL in their storage. And it is really lots of them. I don't think Oracle would be happy about it. One way to twist Facebook's arm could be by offering Oracle for Facebook at a reduced price or threaten to stop fixing/improving MySQL.