The software for this Forum supports private messaging, but SG turned it off.
Given this platform could have it with no development effort, I’d be surprised to see them spend development time adding it to the game — I don’t think their reasoning is inability or priority. I think they just don’t support the premise of having private messaging.
I know why it came up here, but it’s not superbly salient to Beta v31 — so I’d suggest continuing further discussion of it here: Private Messages & Friends Lists, Player Search - Please add your comments & ideas here!