Considering people seem to like having a job, I'd say pretty small.
To be fair, OP did say "
ex video game developer". But yeah...chances are pretty slim. Not only are there at best a couple dozens of people who will have the knowledge to completely built such things on a retail system, I doubt that those who could pull that off on a 3DS would be the same team that could do it on a wiiu (different departments, y'know?).
Still, that isn't the real reason it'll be a snowball chance. And neither is the risk of getting caught and being fired and/or rejected from pretty much ANY OTHER JOB said snitch would be to ever want. No...the real "no way, José" reason is that you don't learn that sort of shit overnight. You're talking about (ex-) employees who have spent multiple years in the company. Who have colleagues, friends or even relatives still within the company. And most likely an ideology (create games for people to enjoy!) that sticks with them even after leaving the company*.
So...you (the OP) think that anyone would want to harm or even potentially destroy everything those other people still work for on a daily basis? And everything he has also ever worked for during that time he was there?
No. I think not. The only reason Snowden did what he did was because the people had a right to know the NSA was spying on them (which is completely correct and justifiable). Healing company secrets so a bunch of ungrateful pirates can hack some stuff is...is...damnit, it creeps me out that I even have to MENTION it. You DO know what "morale" means, right?
*okay, a huge-ass argument with your boss could kind of diminish that...but AFAIK, only a very small percentage of former employees actually hold a big grudge against their former employee. And I SERIOUSLY doubt nintendo is treating their top technology departments like shit