Too soon for games to switch back to something like flash since optical is still cheaper. Having said that though if there is a future disc-less version the idea would be that it'd be digital only and since games have to be installed I could picture it having it's own SD unit that people could take to a gamestop or other such store where they can dump the install files on it and then once you pop it in the reader it'll start to install the game. The idea here is that you would use the same custom SD card that comes with the system and to protect from piracy they can use a custom encrypted FS that only the retailer can copy to with a retailer specific code so they know where it came from. Or you can just sell them with one time install codes so the SD can't be used on another system to install.
The problem of cost is not an issue since people will be using the same card over and over to carry the install media from the retailer back to their Xbox One. Those who have a fast enough connection don't have to bother with this process and say 5-7 years from now as flash prices keep dropping they can maybe move back to it and drop the slower disc method.