Found an active POE splitter that got my attention (here on Ali):
I assume these 5.5mm female DC jacks will fit to them, so I don't need to start cutting of my cables:
That way the setup becomes very solid and simple:
Unless somebody sees something nasty that I have forgotten, I am going to put some stuff into my shopping basket 
BTW on the above link (about the splitters), I see also an example image of a Raspberry being powered via POE:
I assume you will need a more expensive POE switch to be able to power a series of those devices. However just wanted to share it here, because it might trigger the creativity of some folks in this community...
