Well, shit.→
Re-balling? Repairing this is probably out of range for most people with "do-it-yourself"-methods. I couldn't remotely do it.
Never liked the idea of lead free solder for "environmental protection" RoHS. Especially at the beginning devices had reliability problems, and things like cracked solder balls still show up every now and then. Scrap electronics is a question of correct recycling anyway, with lead or lead-free, and stuff failing prematurely is anything but sustainable.
Replacing such chips is a pain in any case. In the end people will throw the devices away and even get the advise
"Just get another one!" which effectively means "minus 1" for the number of units; console is out of production for years.
It would be important to know if the cause is really a bad RAM chip, or something different involved in accessing RAM.