Ludek,
We hope to have some performance data within the next month from some very large sites that are running .LRN / OpenACS with PostreSQL. One of things we need to sort out first is to agree on a common metric. It would also be nice if measurement tools were incorporated into releases and each installation would "phone home" automatically with performance data.
I will let the technical folks speak about MySQL but my two-cents: a) don't think there is a plan; b) and not worth the effort.
