Given that both F and J have been getting increasingly more expensive for the airlines to operate over the years I expect it's a way of removing F by stealth, and then calling J service levels as "first class" in the future. Just think of "BusinessFirst" which I believe both AN and QF had when dom F disappeared. It was a name for business class which gave the impression First still existed.
I expect what is now J will be called F in the future, and what is now Y+ will be called J in the future. Thus leaving 3 classes (Eccon \ Business \ First), but at a significantly reduced cost to the airlines because First doesn't have to be personal suites to compete and Business doesn't need to be flat beds to compete.