While waiting, I looked around and found MongoDB 3.2.6 3.2.10 in the Arch Linux ARM aarch64 package repository. I also found out that the ODROID C2 single board computer supports aarch64. This SBC costs $40 and has better specs (for my DB purposes) than the R-Pi 3. It has a 4-core ARMv8 processor running at 2GHz, 2GB of RAM and gigabit ethernet. It also supports WAY fast eMMC Flash storage in addition to Micro SD. Android and Ubuntu are the officially supported OSs but Arch Linux ARM (64 bit) can be installed as well.