Not to mention the OMAP4 isn't pin compatible with the OMAP3 (and even some OMAP3s aren't pin compatible with other OMAP3s, I think
) to say nothing of how many pins an OMAP47 might have on it
To explain further why your dream is folly, the OMAP is a System On Chip (SoC) which basically means it is a single chip with everything on it: processor, ram, "hard drive", video, audio, USB, "keyboard", serial ports, TV out, everything! By putting everything on a single chip, it makes it small, it makes it cheap, it makes it require less energy.
Technically the RAM and NAND are Package on Package (PoP), which means they're soldered to the CPU right at the end, and a lot of discussion went on about possibly removing them and upgrading. It was considered possible, but you have a very high risk of breaking something in the process, so not recommended, not to mention finding compatible RAM and NAND would not be easy.
The OMAP SoC basically makes up almost half the cost of the Pandora. The LCD screen takes up almost another half of the cost. The remainder, the fraction that is left, accounts for case and assembly, really not a lot in comparison.
To put it into perspective, imagine you're designing a computer. There's a CPU/MoBo combo you can buy for $200, but the CPU is soldered to the motherboard. The individual CPU and motherboard can be purchased in socketable form, with $175 for the CPU and $75 for the motherboard, however. Knowing that the company does the same thing for each iteration, selling a combo board and separate socketable parts, which is the correct choice? Get the socketable one so you can upgrade with every new CPU that comes out (until they do a major update and you have to buy a new motherboard too) or save some money and do the soldered package and upgrade the entire thing when it comes time?
Just looking at the money, you'd have to upgrade the CPU twice on the same motherboard to make it cost equivalent, 3 times to make it cost efficient. Maybe you have no problem updating your CPU three times (even if it doesn't really need it) but suppose you're not just designing this computer for yourself, but for 20'000 people across the internet of varying degrees of experience and interest.
OPT did some surveys and decided that SoC and PoP was the way to go, with full board upgrades when and if it became viable to do so, rather than adding cost and complexity (not to mention choosing an inferior CPU in order to achieve it) for the very small minority that had not only the interest but the technical experience and connections to swap more minor components along the way. That's why the Pandora is not socketable and why it probably never will be.
