Would Linode consider adding the option to directly upload an ISO or DD image to create a 'direct disk' image? Or even a 'sideload' variant to create a disk image from a download URL that points to an ISO/DD image, which would make more sense from a speed/bandwidth perspective if a customer is on a less-than-stellar internet connection.
In essence, it would be the functional equivalent of https://rufus.akeo.ie/
If the 'sideload' option was offered, Linode could keep a list of URLs recently provided, and cache the ISOs for a finite period, Save on bandwidth and storage if some URLs prove popular. If a particular ISO turns out to be consistently popular amongst its users, it may be worth promoting it to Linode's list of images. Not something needed in the first implementation, though.