This article has so much iff about it I have trouble deciding wheather I should laugh at it (specially when it came from an Appleinsider article which had 0 new sources; how is that considered "More claims"?) or cry at the news it brings.
I know I might get a lot of negative feedback, but in any case, let's analyze all the implications of the hypothetical unification of Apple's laptop lines, or even simply of a more-MBA-shaped MBP.
#1 The Optical Drive
Apple is clearly moving away from the physical media. They eliminated a lot of boxed software from their stores, they presented a Optical Driveless laptop (Macbook Air), and they even removed the Optical Drive from one of their previously Optical Drive-holding desktops (Mac Mini).
As alternative solutions, they started handling out OS X on USB flashdrives and created digital platforms and services which allow downloading and/or streaming of content.
Furthermore, even outside the Apple ecosystem physical media is losing some importance. A common evoked argument is one that "music and video professionals need it." Curiously enough, I've read multiple posts from music and video professionals on this same forum stating they have long ditched CDs/DVDs as a fulcral means of storage.
Removal of the Optical Drive is, as such, a reasonable (and perhaps even likely) expectation to have, regardless of a redesign happening or not. It's not the Optical Drive that's stopping the laptop unification.
#2 Storage
This is where, in my opinion, it starts getting iffy.
As is stands, SSDs are still incredibly expensive. Changing from HDDs to SSDs completely would either imply Apple would a) Lower its profit margins drastically, or b) offer much smaller storage space.
Since the former option is a definite no-go for Apple, one questions how smart it would be for Apple to lower storage space offerings. Let us not forget that taking out the Optical Drive basically means we'd rely more on our laptop's storage space to carry our movies, music or pictures with us. How can Apple do that if they remove the Optical Drive? Apple does not still offer a solution that can comfortably counter this issue. And if your solution is "carry an external HDD", wouldn't that defeat the purpose of a lighter laptop in the first place?
#3 Graphics and Screen
Such a massive redesign would have big implications on graphics. Pro consumers need the graphical power for their work, and such a drastic redesign with GPU-withdrawal would cause serious problems on that area.
Furthermore, there have been rumors about a Retina-display laptops from Apple. They really have to up their game (1200*800? Really?), and good graphical capabilities will seriously be needed. I very much doubt the Intel HD 4000 could comfortably process a retina-display 17" screen.
Finally, it has also been well-established that the MBA has laughable screen quality in comparison to the MBP (I'm not talking resolution).
#4 Heat and Performance
The current MBPs are known for heating substancially. Making MBPs thinner would either increase these problems further, or demand Apple to downgrade their laptops' CPUs, possibly even skipping on the quad-core option for 13"s.
With ULV chipsets the problem would be (partially?) solved, but performance would take an important hit as well.
#5 Connectivity, Battery Life
Finally, these are still other things the current MBP line offers that the MBA does not. Unifying the laptop line would compromise both of them.
In conclusion: The unification of MBPs and MBAs would have important consequences in terms of functionality. We're talking about having less storage space for all your files without an Optical Drive to make up for it, less graphical power (would it even be enough for Retina?), lower processing power, lower-quality screens, more heat problems, worse port-selection and lower battery life.
All of that so we could lose a couple hundred grams on weight (which would easily be gained back if we ever needed an external HDD).
In conclusion, I do believe there could be a redesign on the MBP line in order to make it slightly thinner and lighter (something among the lines of the Lenovo U300/U300S line). I also believe the Optical Drive might be going away next release. What I don't believe is that they will make a radical redesign, unifying their mobile lines and abdicating of the entire prosumer market or of their best-selling laptop (13" MBP).