Thank you for replies.

In my understanding, you will support such ROM by software.
I do not hope that you will support such Roms by directly save to SD, because it may cause any access time issue.
Couldn't you use a part of Menu ROM or ZIP SRAM for save area?
Or are there any way to support it by MK3 hardware?
Currently it may be only one games that use 4M flash.
But if the Nintendo realizes that it causes some difficulties to support by a kind of your product, they will recommend it to the game provider.
On the other hands, the device cost-down speed is very fast. The silicon vendor will stop the small size flash, because the cost difference will minimize between 2M and 4M. So I think that such game will increase.
I believe that MK3 is the best solution for this kind of product.