Well, it sorta a cable issue! What happens is the tension of the display cable pulling on the T-CON board causes a solder joint to fail at the cables connection. Apple had a run of bad T-CON solder jobs (likely bad solder) Green/Blue bars being the most common and they happened soon after you bought your system. I’ve only see this one time before and it was fixed under warranty by Apple.
So what to do??? The easy solution is replacing the display on your own $$$ which in my mind is not right.
I would press the local Apple Store to get this covered under a warranty exception condition as its a known issue. But that will take a bit of tactful escalation up the food chain and that might still fail.
The other avenue is to get your system serviced for something else (thats if they didn’t take note of the issue when you brought it in) that way during the QC process its discovered or when you get your system back before leaving the store see if the problem is present and tell the genius this needs fixing.