Not sure about the initial part on what potential is present on the phone, but my opinion is there’s likely nothing there and nothing the FBI needs in any case, it’s pure precedent for future surveillance activities…
After all, the phone is crackable despite what anyone says, even if they can’t find a hack all they need to do is isolate the flash chip, dump it then brute-force it. It’s just that’d have a huge cost in both time and resources to actually do in real-life…