My guess is that (one of the things) they're working on before bringing the new intermediates into service is updating the CPS. Section 7.1 only mentions the X<n> certificates, so I'm guessing they need to add at least the R<n> certificates there before they can be used. So keep your eyes peeled there if you want another hint of when they're about to use the new intermediates.
(And there are even more changes they need to make before using the E<n> intermediates. Actually, it seems weird to me that 1.1 has been updated to say it includes Root X2, while the rest of the document, like section 6.1.5, still says that roots are RSA keys. It's things like that which make me think that updating all the "paperwork" is what's holding up the use of the new intermediates, though I'm just a "layman" and I'm sure I don't know all the steps involved.)