Owners can choose from the two switching approaches. The memory card design is not affected.
Putting it in the external keyboard is not obvious or intuitive, and some 7854s may not have keyboards. I would personally prefer a small mod in the mainframe and a rear panel switch like the original. Others may prefer the easier keyboard change.
On an unrelated subject, it might be fun to change the keyboard id and see what mnemonic the firmware brings up for each key / shifted key. Some day when I have nothing better to do...