It would not be too hard to increase the sequential performance by striping data across more NAND. Random read performance is also not too hard. The hard part is always random write performance. This is because if you want to modify a sector of data, all the remaining data must be moved to a new place. The copying of old data takes lots of time but tricks can be used to optimize them out but for true random writes, the performance will never be that good with the current NAND limitations.