Maybe it helps if I tell you that to my eyes 'optimal' reads strange, it sounds as if this was the recommended / best option.

> I'd like later to have pca in MNE, dSPM etc. but it would do things differently (do SVDs on source time courses). 

Btw. this is something I'm currently working with (using RandomizedPCA), it unveils very interesting things, e.g. clearly shows difference components in the source space I did not see before ... What did you have in mind?