Only thing i would change if possible would be the ability to remove/swap the micro sd card without taking the back off, a little hatch would be great and well if you do consider it
This has been mentioned before - but I believe the issue is one of safety. The Cat ratings and safety design of the 121GW is based on the only access to the meter's circuitry being through the probe sockets on the front - which have been designed to certain standards.
To access the microSD card, you would be given access to the microSD card slot - which is connected to the meter's innards. Such an interface would need very special consideration to be suitably rated - if, indeed, that were at all possible. Since the microSD facility was a "fit in", the restriction on access in order to maintain safety and the Cat ratings is one that will (as I understand it) have to stand.
Yes, it's an issue of access safety.
I know it's a bit of a PITA, but it takes under 20 seconds to remove the boot, unscrew the cover and remove the SD card and insert into computer.
If you need more accessible data logging then I'd recommend a proper data logger. This is a multimeter first with some SD logging capability, not the other way around.
I guess you could always dremel a slot in the back perhaps?