I can’t find a proper workflow to do this:
I want the filling to follow the Subd’s grid…
Even if my hole was planar, I use FillHole and none of the options are satisfactory and I have no idea how to move on from there.
Automatic:
Single Face is the most promising, but I need a tool to be able to add edges. There should be a pen tool to add edges to SubDs…
InsertEdge tool won’t let me insert edges where I need them.
SubD hole not planar.3dm (136.7 KB)
There are probably better ways, but I’d probably just use bridge, then stitch.
It was easy to replicate in a mesh modeller and I don’t even know how to mesh model.
Start
Polygon Pen both sides.
There was a Knife icon called ‘Line Cut’ I got in top view and made two silly lines.
I am not sure I am following how that would look. 
Trying to replicate what I did with the mesh modeller, I created 2 faces with 3DFace (had to click option append and select the subd for both… pretty cumbersome)
Once that was done I was able to insert edges this way:
But even though I appended everything my final SubD is not welded. Anyone knows how to weld a subD?
Use the stitch command
See video of using bridge command. You can also append faces and then split them up, but slower.
Next example:
