After i saw the specs available for the new 21.5" iMac with retina screen, I was really, really disappointed. I had been hoping that they would at least offer SSD as a default drive right from the get-go, but they didn't.....they stayed with the stupid old platter/spinner, and the hideously slow 5400 rpm one at that. Also the other spec in which I was interested, the RAM, was still staying at 8 GB. On the 21.5" nothing was user-upgradeable, either. I reviewed all the specs and the $$$$ and then compared them to a MacBook Pro with the same specs that I wanted and found that the two -- a 21.5" iMac BTO with the specs I wanted and a 15" rMBP with pretty much all those specs already available off-the-shelf at my local Apple store came in very closely together with the dollar amounts. I spent some time weighing various pros and cons and in the end, to make a long story short went with being able to walk into my local Apple store and purchase right on the spot a 15" rMBP with the exact specs that I wanted. This offers me flexibility, too, not just in terms of portability but also in being able to choose and add any external monitor that I want when and if I feel that I need more screen real estate.
I'm delighted with my 15" rMBP with discrete graphics and speedy SSD (512 GB) and speedy RAM (16 GB). This baby is fast and she's also portable. I have options, too, with regard to increasing screen real estate in the future if I need to do so. VERY important to me.
I'll never go back to a platter/spinner hard drive. SSDs blow those right out of the water. My once-loved 2012 iMac with a platter drive is now in the hands of a new owner.
Apple really disappointed me and I'm sure a whole bunch of other prospective customers by the way they chose to configure the base and next-to-base, available-in-store 21.5" iMacs. For me, the baseline spinner drive doesn't hack it. Also, sad to say, for me, again, Fusion Drive just doesn't hack it, especially with such a small SSD drive provided. I want pure SSD with enough capacity to actually run my machine and more. Sure, a lot of people would have simply shrugged and moved right on over to the significantly larger and heavier 27" iMac, but for various reasons I could not do that and did not want to do that.
For me, going with the 15" rMBP fulfilled my needs, but of course that is not going to be the same situation for everyone. As far as hoping for and waiting for Apple to put 21.5" iMacs into the stores which do meet your particular tech specs, I wouldn't count on it. Probably Apple won't provide SSD as the default drive in their iMacs until the next iteration or maybe beyond that.....