While no one knows for certain, probably not even asus, when broadwell and maxwell will make their debut in the laptop gaming aspect. I would easily guess it'll be at least late next year more than likely the year after that.
If broadwell follows any sort of suite with the rest of the upgrades, then expect 5-10% perofrmance increse. Broadwell biggest hype will be battery life, but in gaming laptop with better screens and power hungry gpu's, i doubt battery life with broadwell will hit even an hour longer.
If maxwell follows suite, you can expect a 10-15% performance increase in same tier chip comparisons, and again maxwell is aimed largely at power consumption, not performance increase.
I have the JS, kind of wish i went with jm as thats till a beast, or the jz which is the best you can get. But i went mid tear and bought ram and ssd instead. 2x 1tb samsung evo and another 16gb ram. I felt that was the better way to go for me personally. But i do rendering video editing more often than gaming.
But gaming wise, when i had the jm model, i played every game at worst high settings. My JS model, there hasnt been a game that hasnt been ultra. Those are bf4, cod, titanfall, skyrim, ect. I cant image there being a game coming out soon that would play at medium settings on these machine. js or jz. If your that worried, then get the jz model, up 15-20% from the js model.
As for 4700 not being enough, i have yet to have a game hit even 70% cpu utilization, normally not even hitting 50%. With newer generation chips adding maybe 10% performance increase, instead of playing around 50% you'll play at 45%, alright. I render with mine like all the time, thats 100% cpu, 100% gpu, and not quite as fast as my desktop, its really within a few minuets of rendering an hour movie. Its really really close. And my pc is a 8350 overclocked to 5.0ghz with a gtx 770 (in sli but rendering doesnt care about sli).
So, i really dont see the need to wait for a year maybe two to get an added all around 10% performance increase. Lately newer laptops are just adding 3k-4k screens which are great for everything but video games and is awesome, but its really to a point that laptops can play high/ultra so how much higher can you get?