That was false, as the internal storage is actually an eMMC chip.
However, I bought a XT1032 model, with 16GB of internal storage, and, being a ruthlessly enthusiastic electronic engineer, I decided to take the matter of SD card support into my own hands.
I noticed, shortly after getting it, that my phone, being the single SIM variant, has an unused slot in the side, and, upon closer inspection, no important components around that area.
So it began; turning the unused SIM slot into a microSD slot.
I first went to PC World, and bought this tiny USB card reader:
I then stripped away all of the plastic, and all of the metal USB connector. I was left with this:
I then took the microSD slot from an old phone:
The above image shows two contacts in the top right corner which are pressed closed only when the microSD is present.
This is crucial to the operation of this mod, because it enables me to distinguish whether the SD is present or not (more on this later).
I then glued the card holder to the reader circuit board:
I used pliers and a scalpel to remove the unused SIM holder, and scrape an indent in the phone's pcb, to give more space to the reader circuit:
Finally, I soldered (VERY carefully) the relevant connections to the inside of the phone's connector, used a scalpel to cut away any obstructive plastic, and cut a copper sheet to fit over the SoC, RAM, eMMC, etc.:
And then put it all back together. I powered the phone up, and used a charger and a 2GB microSD to test everything, and hey presto, IT WORKS!
This mod takes advantage of the USB OTG function of the Moto G. My modifications, while extensive, are essentially an "Internal, Switch-able, OTG microSD Card Reader".
This is where the card holder contacts I mentioned earlier become important. The phone uses pin 4 of the USB connector to detect what is connected. A certain value of resistance between pin 4 and GND tell the phone what a connected device is. For charging the phone, or connecting it to a computer, pin 4 needs to be dealt with by the computer or charger. We cannot interfere with pin 4 in these two situations.
If we kept pin 4 low, the phone would try to constantly power the SD card reader, and so would not accept a charge, and would soon run out of battery. The solution is to only enable OTG when the microSD is present. This means that for charging, I take the SD out, the switch on the connector opens, letting pin 4 be controlled by the charger/computer. The phone can charge up, and when it's finished, I put the SD card back in, and OTG takes over again.
Many thanks, and I hope you enjoyed reading!