Ok, it seems that MySQL AB is finally committing to fix up PDO_MySQL and to generally accept the fact that PDO is the future. Of course mysqli will also be actively maintained. But they will also make mysqlnd play nicely with PDO etc.
They have a budget allocated for PDO development. They will soon assign a developer on this I am told. As part of this effort it is expected that the entire PDO test suite will also benefit.
Furthermore they have allocated someone from the doc team to check over the ext/mysql and ext/mysqli docs. I will poke the relevant people at regular intervals, that any MySQL specific features in PDO will make it into the docs.
I was waiting 2 years (at least) for this to happen. Thanks for the good news, Lukas :)