This really does baffle my mind, more so because the framework is already in place and all Netflix has to do is literally put in a few lines of code enabling it. It's been out for far too long for them to have any excuse not to support it.
If you want to be more proactive, you can actually send a message / complaint to Netflix directly. I know a couple of people at Netflix where they actually analyze complaints of just about anything and can sort them by how common they pop up. Enough demand for PiP in their system will get their mobile developers going on it.Sometimes you just need to bitch...do I expect Netflix to see this? No, but sometimes I just want to share my frustrations and see if I am the only one.
... which is?
All options out there are mentioned here.There are a few
I use tubex but I remember protube being listed also
Not 100% sure about ads although it seems there are none but you can definitely play audio only and in the background with TubexAll options out there are mentioned here.
There are a few third party apps (ProTube,YouPlayer, Tubex) which do offer this Slide Over/Split View, Picture in Picture (PiP) and even have other great features (play audio in background, remove ads - ProTube only).CornerTube, Moldavite only offer Picture in Picture (PiP).
My favorite is definitely ProTube.