Originally Posted by X-Men
Given that one of the big advantages of the retina over the cMBP is the retina's SSD flash drive,
I don't see that as a big advantage in the current machines. SSDs are readily available for use in all Aple laptops.
is it possible (or practical) to replace the optical drive in a 2012 cMBP with an SSD drive?
Third parties support this.
And if so, is the only option to do so through Apple, or are there less expensive alternatives?
Apple doesn't support this.
If this is a realistic option for down the road upgrading,
It isn't a realistic option in my estimation. The Problem is SATA is dying fast, anybody with any sense would go with PCI Express in new machine builds. That for performance and to eventually eliminate SATA support from chip sets.
it makes the cMBP even more attractive vs the Retina, which seems not to have any upgrading flexibility.
That is an issue with the retina machine. I'm not sure if poor sales for that model has taught Apple anything. By the way I wouldn't expect support for legacy secondary storage expansion. Rather I would expect to see another of Apples PCI Express based expansion slots in the machine to allow for two or more blade devices.
In any event you need to evaluate realistically what your storage needs are. If you think 200 GB is enough, double it and see what Apple offers. By the way, experience with my old 2008 MBP tells me that 200 GB isn't enough for most users. It certainly isn't enough if you intend to run virtual machines.
Personally I think focusing on upgradability these days is the wrong way to look at computer purchasing. The problem is the rapid improvement to the hardware means that you are throwing away good money on anoint hardware. It is far better to make a purchase with the intent of keeping it as is for several years. Where several years revolves around 5. That means buying a machine with enough RAM and secondary storage up front and working with that until new hardware becomes compelling. A wise move here is to make sure those sizes are fat to keep you in good order for all of those years. As mentioned above that means buying more RAM or secondary store than you think you need right now.
In any event I'd think long and hard about the value of "upgrading" in today's technology markets. It isn't like you will be doubling performance every six months anymore. In fact I honestly believe part of the problem with the massive slow down in the PC market is that people don't see the value anymore in quick upgrades. A computer that is 20% faster does nothing for reading E-Mail, surfing the net or the other things commonly done with PCs. When the time does come to upgrade it might be six years down the road. At that time technology will have changed so much that it is far wiser to buy a new machine. By the way six years isn't all that long anymore, just look at all of the machines still running XP. It really is a different world these days.