Personally, I think that improving the SD reading speed is the way to go for the future.
Let's face it, even if they do a 1024 Mk you still will be limited to flash 1 game at the time(if it's a large game, but this is what we are talking about) and it will take a long time to burn it to the flash memory.
And then eventually bigger games will come out, and at that point we should all buy a third,bigger MK.
If SD reading speed gets improved(which can be done completely in software) we will be able to play games right out of the SD card, with no whatsoever size limits and burning waiting times, this way even if bigger games come out, we won't be needing extra hardware.
However, if SD speed remains this low....I am afraid I will have to look somewhere else for other solutions.