Only if someone can throw light on, between a Pencil and 3D Touch what is more useful from a usability stand point, will I be able to decide what to let go and what to keep ! And that will help me decide better !
You probably won't get a choice which to let go.
If the iPad Air 3 has pencil support and no 3D Touch then you can choose to buy it and not get 3D Touch. But you can't choose not to get pencil support because it's already there
I think if you're looking for consensus then even in this thread people are saying buy the new one in a couple of weeks. Not because 3D Touch is a waste of time, but because the new iPad will be a huge leap over your current one and will easily last you 2-3 years.
So what if 3D Touch comes out in 12 months? So will features X/y/z that you don't even know about - there is always something better around the corner
I personally don't buy into the hype around 3D Touch being a game changer like multitouch was. That is hyperbole from Apple and simply ridiculous. It is a nice feature that lets you do some things a bit quicker. But it is nowhere near the paradigm shift that multitouch brought.