With a bit of digging, I found that:
-news of RS not being able to receive older Pokémon was in early October 2002, nearly two months before release.
-confirmation of DP being able to receive Gen III Pokémon was among the first DP news, being revealed in CoroCoro in May 2006, four months before release.
-and as I said, the Poké Transfer Lab was revealed about two months before the release of BW.
So we might expect news on that front sometime between June and August, if not later.
From: AzureKite18 | #010they just havent announced it yet because there are bigger topics to address.
Basically this.