First thought that is one of these max clocking pissing contests. And while it might be, I see that skinflint (aka geizhals),
list 63 DDR4 modules over 3733. Of course they all cost a fortune with the cheapest being £10+ per GB (without filters, the cheapest DDR4-2400 modules cost £2.71 per GB).
Of course, chances are performance won't improve that much unless people run 7Zip all day (or maybe Fallout4). Now, when the APUs come out it might be worthwhile having such fast ram although if AMD were to release a high-end HBM2 APU it is likely to work cheaper than buying extremely expensive RAM.
Which raises a question: what z height would a APU with HBM2 be? And if it is higher, has AM4 got enough hight? If not, we can either conclude AMD are not going to release and desktop APUs with HBM2, or someone messed up when designing AM4.