Lack of End Game Content

[Dualblade]

If that's all your interested in then I doubt SE will ever be able to make enough content to keep you playing. Also won't there be a new Ultimate in 5.1?

Most likely but it is possible it'll be 5.3 and 5.5 instead. The only thing hard confirmed is more MSQ and the NieR 24-man, everything else is based on "this is how SE usually does things for this game".

But yes presuming Ultimate comes 5.1 that'll (assuming he is right about himself and he doesn't get stuck still trying to complete it before 5.1) he'll have two months of "nothing" for end game.