Well it's big and heavy and doesn't fit on travel tables in planes and trains. Apple redesigned in 2012 that is only 3 years ago by your own reckoning it'll be 2017 for a redesign.
It's not that big. You're acting like it's a PowerBook from 2002 or something. It fits fine in travel tables and planes, I've had one. The rMBP is quite nice, but its not THAT much thinner than the 2001. Quite thin.
There's no way apple will wait until 2017. I've been following Apple for about 20 years and know how they work. They want to get rid of all the excess. They want to move to USB-C really badly and unify all of their products and their manufacturing. 2017 moves into 10nm CPU manufacturing and it won't be until 2019 that these processors become a reality. Skylake is essentailly a SoC now because the PCH moved onto the die, so Apple has more room to wiggle around. They can get rid of USB 3.0 ports and the MagSafe port and make the rMBP way thinner. They can also get rid of the bigger fans, have smaller batteries and possibly downsize the display bezel.
Apple usually makes smaller products first then moves it to their bigger brothers. The new MacBook 12" is a revolutionary design and they would move it to the rMBP.
Watch next year, 2016 is the year of the new rMBP.
I honestly don't care, I like my rMBP a lot, it's light and very very fast. the 750m is not the greatest dGPU for me but its enough. I wish they would move to the 960m at least. Maybe they will soon. Those GPU's are also very light on energy usage and heat.