If SD cards were still limited to 16/32mb/real low amount then it could take more cards.
Here's the thing - Even with the size increases to their data that comes with a new gen, it's still not going to exceed a kb per pokemon. Right now, pkm files? 136 bytes. Thats all the data for one pokemon. It doesn't have to store it's graphics, it's sounds, or the graphics for it's attacks because that is included in the game. All that the file stores is the identifying information for the pokemon - Id numbers, levels, moves, those kind of things. Even if it jumps to a full kb, this still wouldn't take up a whole lot of space. Well, any space really due to the size of memory cards now. We've cards that go up to 128 GB now. But still, a common 4 GB card would be more then sufficient. Hell, even a 2 would be.
And a regular SD card isn't coded for anything. It's designed to hold data, any kind of data. As long as the data is, at it's core, made of zeros and ones the SD card could care less what is put on it.
The same applies to all memory cards. The only major difference between cards is their storage space and shape. While some preform better then others - faster read/write rates - they are all of similar performance. Micro, Mini, and SD are all the same type of cards really - Just diffrient sizes for diffrient electronics.
And memory corruption? The same can happen to the data that gets stored in their services. The storage medium that they will use will be susceptible to corruption the same as any memory card. Hard drives, solid states, hybrids, flash... Doesn't matter. All are susceptible to corruption.
Conversion will take space but mostly for the conversion app. And even then, the program isn't going to be that big.