I've tried to download the SDK via Google Drive (4 times !) and unfortunately it always fails after the 3Gb point which is very frustrating! It is possible to split the download into smaller chunks for download. Furthermore there doesn't seem to be any git mirrors available.
Some suggestions:
Could you include the SDK tar file as part of the Ubuntu rootfs (on the eMMC) ?
Include the SDK (plus eMMC backup image) on a DVD with the board.
To download the SDK I resorted to installing gdrive-tools and copying the SDK to my Google drive account. Then using gdrive-tools to sync my Google drive with my local machine.
