The NES Classic Edition has already been hacked, and right now, it is already possible to expand the number of games that can be put on the device. But despite this, it doesn't really change anything for the future of the NES Classic, and here's the reason why:
Can you actually buy one right now?
If you are unable to acquire the NES Classic Edition, then it's pretty clear that won't be able to hack it. The biggest story for the NES Classic Edition remains the fact that Nintendo still hasn't been able to meet the growing demands for one of its most popular (as of the moment) console.
Simply put, there isn't going to be a huge amount of hacked devices until there will be a huge wave of the console for people to actually buy.
Do you really want to risk it?
There are already videos and online instructions circulating, detailing just how exactly you can open up your device to be able to add more games. But the entire process is a bit complex and intimidating especially if you've never done hacking before. It's not that it's that hard of a deal to be done, but the point is, after seeing the instructions and the longevity of the process, most casual fans will give up before they even get started.
Nintendo has already accomplished its goal
Nintendo not only knew that its system would eventually be infiltrated and compromised, a programmer for the console has even left a message inside the device's code for anyone who would go looking for ways to open it up.
By the time you've bought an NES Classic and worked on adding more games, Nintendo has already made more money on you than it would have if you just pirated all the games you intend to play and used third-party hardware instead for your emulation box.
The future of the NES Classic and every other retro console that will be coming is pretty high, and it wouldn't take hacking the console to change it anytime soon.