I recently upgraded my rMBP mid-2014 (2.8 Ghz, 8GB, 256GB) to a slightly younger rMBP early-2015 (2.7 Ghz, 16GB, 1TB). I did not anticipate the disastrous MBP-redesign and became aware of it only earlier this year when I started looking into upgrading my mid-2014 machine. Everyday tasks were still running buttery-smooth like on day 1, but the 8GB memory caused some stutter in large data sets and I was running out of space on my SSD. I quickly realised that I was not willing to pay a premium to give up ports (I use the SD-card slot almost every other day), Magsafe, acceptable keyboard quality and the overall reliability of a refined design.
At the point of my realisation, I could not find any new 13" rMBP early-2015, but believe me, I tried... I called up Apple resellers all over Germany, Austria and Switzerland for weeks. I would have gladly bought a maxed-out early-2015 despite it being no longer state-of-the-art, with Apple Care to make sure it's going to last till Apple moves on from this current, anorexic MBP design. Despite my failure to source a brand-new machine, I was lucky enough to find a 1-year-old barely used rMBP early-2015 at a great price. The processor is slightly slower than the one in my rMBP mid-2014, but I haven't noticed this in any of my tasks. However, I have felt a considerable boost from the 16GB RAM and the 1TB SSD is a god's end as it means that I have no longer to work with a permanently attached external hard drive. My rMBP mid-2014, I was able to sell for € 900 and the rMBP early-2015 set me back € 1200. So, my upgrade cost me € 300 in the end.
I'm sorry, Apple discarded the tried and tested rMBP design for its current joke of a pro-line. Of course, they need to further develop their products and can't stick with one design forever, but I feel the current Macbook-lines are mostly a step back, rather than a step forward. With this in mind, I don't see myself upgrading again until my current rMBP bites the dust.