It seems developers still have to implement a specific controller/something for that. I thought you mean something different where it would all be somewhat automatic.
That's exactly my point. When it was announced it wasn't obvious that this didn't come for "free" and I am saying the new dual pane feature is likely to need the same such implementation which won't attract developers.
iOS 8 with the launch of iPhone 6 Plus promised to allow developers to make their portrait mode apps also run in landscape mode on the larger device.
No developers actually made use of this feature, so it's pointless.