Yes, it would be welcomed... but we don't know if or when. This is complete speculation. I've got photo editing to do today, this week, next month. How long can I wait for a machine that may never materialize? The Apple waiting game is such a waste of time. If computers are a hobby for someone, great, it won't matter when or if the next "revolutionary" or "magical" item comes to fruition. But working pros can't make their buying decisions based on their own personal wish lists. That's a great way to end up with no computer. Ever.
Yes, and that's why most people who use computers to do real work use PCs instead of Macs. The Apple approach is very much towards consumers.
Sure there is! Buy the upgradeable one today.

I get it. It's all about tradeoffs. If the Retina display is more valuable to you than user-upgradeability, so be it. Decision made. I went the other way: the glare involved with the Retina is a bigger cost than the extra pixels afforded. This was a con, not a pro. Not to mention the screen ghosting. So the new glorious screen was actually strike one. The lack of expandability was strike two. I didn't need a strike three. But if I did, it was the price of the Retinas.
Well, actually, for me, the retina display is a must-have and much more important than any user-upgradeability, as the rMBP already has everything I want in a laptop. So, my decision was already made even before the rMBP was just a mere speculation here at the forums of MacRumors.
But, for those who need user-upgradeability, it's a matter of trade-offs as of today. Everybody knows that Apple will discontinue the cMBP sooner or later. You may not like it, and lots of people seem to hate Apple for that, but Apple will probably do it anyway. So, choosing the cMPB over the rMBP because of its upgradeability is just a temporary solution. You buy a cMBP now, but when you're on the market for your next laptop within a few years from now, when the cMBP is already discontinued, what will it be?
That's why I said there's nothing I can do about it.
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Let me explain then? Beside having Retina and SSD, rMBP IS a lesser machine in some ways. It's an disposable iPad in disguise of a Mac.
- Pairing retina resolution with midrange GPU like 650M or Intel HD Graphics is not a good decision. You have a good screen but you can't do anything intensive with it either. Sad.
- You only get expensive or low capacity SSD options instead of cheaper HDD or hybrid solution. Even if you insist pure SSD, it's not really that expensive nowadays. Meanwhile Apple still charges us much more than it should.
- Onboard, soldered RAM while it's the cheapest and (used to be) easiest way to make your laptop performs a bit better. Not only it shorten the Macbook lifespan, also it requires you to pay (unnecessary) top dollars for RAM sticks from Apple, should you want more.
- Replace something out of warranty on rMBP is super expensive and uneconomical. You can't even replace the battery or built-in trackpad without buying the whole bottom case, which is unnecessary?
See? .. it's a lesser machine in many ways than cMBP.
Your biggest point is about user-upgradeability. Being user-upgradeability, the cMBP may be updated to feature an HDD, an SSD, a hybrid drive, or even both, if you have a 15-inch cMBP. You may also replace the battery or increase the memory.
You can't do any of these things with the rMBP. It doesn't make it a lesser machine in my view, but this is certainly the biggest point of concern of Apple's users, and they're just right. It's the biggest trade-off when you choose a rMBP.
That only reminds me that we're all at Apple's walled garden, and that we must swallow the closed ecosystem and the impenetrable hardware if we want to benefit from the wonders of it. Kind of selling our souls.
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Have you opened a rMBP up? It's batteries all the way down.
I know that. I also know that Haswell will consume far less battery than Ivy Bridge, so a Haswell-powered rMBP won't need so much battery as the current rMBP.
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Yah. 19" is just wishful thinking on my part, but I agree that Apple will probably release a 17" again when a retina display for that size is more feasible. I hope.
While it's a possibility, I wouldn't count on that.