Unfortunately General is right. You can build modular notebook but not such integrated device like phone. Connector itself will eat too much space and additional cost. On the other hand - would anyone buy n8x0 two times thicker to fit ie. GSM module with additional battery? If one does something removable - it takes additional space and design to make it swappable. Take Apple devices for example - they took it even further - devices are slim and small without possibility of replacing battery. No one really wants bulky "future proof" devices.