Let me put this another way: Do you think the developers behind editline wrote it because they wanted to violate the GPL? Or did they write it for some other reason?
Personally, I read the Sony post very differently. It sounds to me Sony, in part because of the aggressive stance SFC takes with busybox GPL violations, isn't happy with the business costs of using busybox (e.g. concerns among chip vendors and suppliers). They could easily be wrong in their assessment of the business costs (e.g. concerns from chip vendors and suppliers should not be taken seriously), but given that assessment, it seems to me that writing a busybox replacement is a reasonable response.