Admittedly I've painted a somewhat bleak picture so far in regards to a future where all consoles are disc-less: game retailers struggling to stay relevant, and the secondhand market perhaps simply winking out of existence altogether. It isn't all bad though by any stretch, because there are plenty of upsides about a fully digital distribution system as well, as long as it's handled intelligently and steps are taken to ensure the transition goes smoothly.
Although the secondhand market might encounter a lot of problems, one of the upsides to digital only distribution is that games will become cheaper; with no disc or packaging to manufacture, no manuals to print, and no shipping costs to cut into profits, the games can be sold with lower overhead than is currently possible. Publishers can sell a game directly to the players that want it, and reap 100% of the effective profit. This is a major incentive for publishers and developers to get behind disc-less media, because it will actually help bolster profits off of each sale, while keeping the price point competitive.
Another upside to digital media is a greater incentive on the part of companies to make sure that their games are working right and kept up to date in terms of patches and updates. There's already not much of an excuse to push out a game that has obvious bugs in it, but if something slips past the testing and then is only found after the game goes gold then currently companies have no choice but to put out a day one patch -- something that doesn't earn a lot of praise from the gaming community -- but with digital only distribution changes can be made much later and closer to the release date without as many potential problems cropping up. Since the games will also be more online involved simply via being sold through the internet, the developers can also keep a closer eye on what needs attention and what's working well.
In one of the better scenarios, the move to digital only will also help bridge what seems to currently be an ever widening gap between developers, publishers, and their actual audience: the gamers themselves. It's a strange but notable trend that companies currently seem to see the very people they sell to as at the very least unpleasantly adversarial and at most outright venomous and contrary. Gamers don't tend to view the companies much better in a lot of cases, with most coming off as giant monolithic creations that don't really care about the content or enjoyment that games bring over the almighty dollar. A disc-less future will in some ways force these two groups closer together, and hopefully also assuage some of the more negative feelings that each has about the other.
Regardless of any of that though, what we're experiencing now, with the mix of discs and downloads, is merely the start of a trend that's going to continue to rise more heavily in favour of the latter as time goes on. It might even be possible that we'll see more gamers embracing a purely digital library even when the physical media is still available. Odds are that until given no other choice that we'll never be disc-less entirely, but perhaps the current trends will help acclimate us all to the days to come.