Well D4 IS declining. PoE IS probably growing a Lot in full Release.
Not saying PoE geht’s ahead. But i dont See Them Miles apart. And in a couple of years with mediocre D4 addons and good PoE addons i See a Chance for PoE to Beat D4 fair and square. If IT Happens ITS years away, but i would Not rule IT Out. Blizz IS failing too much atm.