Improve grid fill

(2) Use triangle on last edge instead of asking for "2 edgeloops".

This one thing is verrrrrrrrrrrrrryyyyyyyy annoying...

It sounds like you need to select one side of the edge-loop, then extrude this ‘extrusion front’ inward the hole while snapping to the neighboring 2 vertices in the edge-loop and repeat this process until the hole is completely filled. Then merge any overlapping edges along the edge-loop. Imagine that you have a perfect rectangular edge-loop to fill; just select the top row and fill downward.

It is less obvious with more organic shapes. The art is in the extend of the initial selection: a too broad initial selection causes the ‘extrusion front’ to collapse onto itself in the final iteration (causing many triangles) while a too narrow initial selection causes the ‘extrusion front’ to have to fan out (causing an n-gon). Maybe, some heuristic can cause the extruded edge to intermittently (locally) collapse or split (introducing triangles or 5-gons respectively).

You might want to adjust the location of the filled-in vertices and their normals to fit the curvature of the edge-loop. The exact method for this could be configurable (e.g.: flat, bezier, ...) and influences the collapse- and split-heuristics.

In an alternative implementation, one could run an n×n search for an automatic initial selection that yields an optimum (e.g.: minimum #vertices, #edges, or #faces, minimum curvature, ...)

I have been thinking about this last night. This is really useful.