looking into how to properly erasing data from solid state devices is quite the topic with a different answer from just about every webpage I read. I understand there are issues with wiping data from SSDs due to the efforts of wear leveling, but now I read that eMMC supports TRIM, does that mean that eMMC storage will be just as complicated to data wipe as SSDs are?
I don't believe TRIM has a major effect on memory clearing; it's wear-leveling that's the main issue, as it means the OS could 'overwrite' data while it still exists on the physical media. TRIM is just telling the drive that a certain area isn't needed, and the drive can do what it likes with it.
SATA drives (including SSDs) have the ATA-SE commands, which allow you to tell the drive to delete everything on it, including any 'reserve' areas. Whether this is implemented correctly is another question, though. I don't think eMMC drives have this.
As eMMC drives are generally a single package, it's harder to remove the flash chips (or solder onto the pads directly) and read the flash without going through the controller - this could make it slightly more difficult. It's probable that eMMC controllers have debug modes that allow read-out of the flash, though.
I'd have to agree with childofsoong that you can't be certain that it's all gone without complete destruction.