1. There were hacks for iPad1 upgrade RAM by replacing the Soc chip from an iPhone, it simply works. (since the SoC was used by other iOS device anyway)
2. It really is possible to "desolder" the flash memory chip off the device, by tracing back the pins and specs, it is possible to put a larger chip in the device, tech also needed like pre-flash the chip with data / FS, changing system boot kernel param, changing boot scripts etc.
3. for device as user kellyhk mention, that is much easier, get the internal SD card out, dd it to another larger card, extend the FS volume size maybe.