Quad core 13" laptops are likely for later this year IMO. The Core i7-8550U is a 15W CPU already released and is available in Razer's Blade and Dell's XPS 13 (2018).
Hopefully Intel will have their Quad 25w parts with Iris Pro graphics available in time for the next MBP release.
Regarding DDR4, I don't think this will happen this year. Intel's website lists the aforementioned CPU supporting both LPDDR3 and DDR4, but doesn't list LPDDR4. Apple won't make the battery life sacrifice that comes with not using low power RAM.