If I want to share the Sparky goodness and give away a core to a friend, how do I release my claim on it in the cloud ?
I can do a factory reset on the core itself to reset the firmware, but I assume the device ID remains the same and so there is some step I must take to release the device id, so my friend can claim it when they receive it.
And as if by magic - a “remove core” button appears on the “cores” page under build - would that be all I need to do ? remove that and factory reset/forget-wifi reset the core ?
Good timing - that feature was just added 
No need to even factory reset the Core; all of the “ownership” state of the Core is managed in the cloud, so once it’s unclaimed, it’s immediately claimable by someone else.