I always liked to keep the things clean, so the idea of having development environments for both KDE SC 4.x and KF5 on the same machine was not something that thrilled me. Apart from that, when I realized my versions of mesa+xcb are crashing the new plasma, I decided to go to the other side - the weird side.
My laptop is now dedicated to the new plasma developments, while my main system remains on the 4.x branch.
The problem is that the laptop is much slower than my main machine, has a small screen and keyboard which makes writing code on it painful. That is why I don’t use it directly - I work on my main system, while everything executes on the little guy. Everything, but compilation. Thankfully, the icecream distributed compilation system works without a glitch on any distribution although it was created by opensuse KDE people (kudos!).
I have to say that this is perfect - I can crash anything ranging from kded to kwin and plasma without interrupting my workflow, and can test plasma on a slower device so that I don’t introduce some big performance issues that I wouldn’t even notice on a real computer.