For a lot of users 16GB might not be worthwhile, 64GB might actually allow some people to not use a SSD at all, so it I think they will have to provide 32GB of storage. That seems obvious enough that the fact it's not stated in the article seems somewhat concerning.
If they release it next year and it turns out well, I can certainly see Apple pulling such a move for the MacBook (Air).
"Each megabyte of 3D Xpoint will certainly be significantly cheaper than the equivalent amount of Ram. And the new technology has the added advantage of being non-volatile, meaning it does not "forget" information when the power is switched off. But, unfortunately it is still not quite as fast as Ram, and some - but not all - applications need the extra speed the older tech provides."
What can be read from the announcement: it's not as rewritable as DRAM: only up to 1000 more writes than NAND. It's also slower than DRAM. But it seems better than NAND in all aspects.
Err, they mention several times the density of NAND.