We are happy to announce that we now have an unofficial Pi3 64bit image at:
This allows users/developers to experiment with the ARM 64 bit architecture easily. The Pi3 and later model support this mode. It is an unofficial image, which means the task that requests a sertial will fail (visible in snap changes). Note that for production use the memory on the pi3 may be a bit low.
You can write to an SD card using e.g.:
$ sudo snap install godd --devmode --beta
$ godd -
[this will list the available removable devices]
$ sudo godd http://people.canonical.com/~mvo/unofficial-pi3-64/core18-pi3-64-20181105.img.xz /dev/sdX
[replace sdX with the actual device]
(or your favorite other method).
Please let me know if you notice any issues.