Attached is update to ConeUnwrap script.
The .js is considerably shorter.
The .htm is a little larger, with a bit more detail in the prompts.
The math is the same.
The orientation of the cone/frustum in space does not matter. Lengths are used, which are positive numbers.
The Bottom and Top of the frustum can be picked in either order. If Top Length is greater than Bottom Length, they are swapped.
Substitute Bottom, SlantLine, and Top circles can be used. A substitute Slant Line can be placed anywhere the SlantSeam would rotate around the center axis of the cone/frustum, which could help avoid holes. (A rewrap cone would have a relocated slantseam.)
A portion of a cone/frustum made by trimming with two SlantLines, can also be unwrapped to a Net, using matching Bottom arcs and Top (for frustum) arcs.
The Base and Top circles/arcs do need to be planar, and the cone/frustum "right circular."
Thanks again to Michael for his help and hints, and borrowed .js and .htm code :-)

With subsequent Flow unwrap of addition surface curves/edges/holes, the user will be responsible for verifying orientation of everything.

- Brian

ps If all goes well, I'm going to do ObliqueConeUnwrap next, which will include elliptical or circular bases, or portions thereof, provided they are planar.
The equation will require numerical integration, which is already available in another script, and interpcurve.
The Oblique script should also work with cone-like objects with "radial" "ruffles" or wrinkles along the SlantLines (I think.)
The object will have to be developable, and have an apex point, although subsequent Flow should handle frustums.
(We'll have to see how the bottom edge turns out.)

Thanks Brian !

After a lot of revision, here is the script _ObliqueConeUnwrap,
which creates a planar "Net" of the unwrap of a cone-like surface.

Reference: https://plus.google.com/+NilesJohnson/posts/jCmg66wyo83

The MoI .pdf file "ObliqueConeWedgeCut" shows Niles' ascii drawing, in a more comprehensible fashion,
from which comes the equation he uses in the SAGE program, based upon the pythagorean equation.
dTheta = Math.sqrt( Math.pow( dS, 2 ) - Math.pow( dR, 2 )) / R;

The script should use 500, 1000, 2000, or more points, for a "brute force numerical integration."
The unwrap curve is not "perfect," but the "tolerance" changes for more points.
Rebuild can be used. It was not necessary after all, to use Trim in the script.

An ObliqueCone is easily made in MoI by extruding either a circle, or an ellipse, closed or open, with command Extrude, using "To point" and "Unlock direction" buttons. The iso-curves should be uniform. The cone can be a right circular cone.
A cone-like surface may also be made with Extrude / To point / Unlock direction, using some other curve.
These surfaces are also candidates for _ObliqueConeUnwrap.
Possible overlap is ignored by the script. The script just needs an apex point, and a base curve.
The base curve may be a standalone curve, or an edge, and be closed or open.
The base curve could be nonPlanar, or sinusoidal. After the unwrap, if a center line from the Net center point is added,
Network can create the planar surface, with nice iso-curves that can match the iso-curves of the cone-like surface.

Placing a sphere at the apex, and doing intersect, makes a base curve which could be nonplanar,
The unwrap may be an arc of a circle. All of the "radial" line segments are the same length, and dR is zero. dTheta = dS/R.

- Brian

Hi Brian,
lot of work here !
it will be nice if you do a little video to show how to use this script
Also , i can't see your script in attachment
Thanks a lot.

Hi Finema,
Script is now uploaded. (I did a last minute minor edit.)
I'll have to learn how to do a video...I did buy Camtasia a while back...

I've decided that the sphere intersect of an elliptical oblique cone has radials at equal curve intervals (untrimmed segments), but that
delta theta angles are NOT quite equal(?).

- Brian

Unwrap of Extrusion of Circle or Ellipse

Define a simple extrusion as being along a line, without using curved "Path," "To Point," or "Tapered" selections in MoI Extrude command.
For such extrusions, the top curve will be of the same character as the base curve.
Reference for "Net of oblique circular cylinder" Niles Johnson:
https://plus.google.com/+NilesJohnson/posts/WsmXBbu3Vu9

A right circular cylinder is the result of a simple extrusion of a circle along a line perpendicular to the plane of the base circle.
Similarly, a right elliptical cylinder is the result of the simple extrusion of an ellipse, perpendicular to the base ellipse.
The draft angle in these cases is 0 degrees, (plus or minus multiples of 180 degrees). (So angles are modulus +/- 180 degrees.)

For other draft angles, excluding the flat case of 90 degrees, "oblique" objects result.
An oblique circular cylinder is the result of extrusion with non-zero, and non-90 degree, draft angle, and has an elliptical cross section.
Slice planes parallel to the base result in iso-line circles parallel to, and equal to, the base circle.
An oblique elliptical cylinder is the result of extrusion of an ellipse with non-zero, non-90, draft angle.
Slice planes parallel to the base result in iso-line ellipses parallel to, and equal to, the base ellipse.

Curiously, note that removing the base and top of a circular cylinder with a matched pair of non-parallel slice planes, results in an oblique elliptical cylinder, not an oblique circular cylinder. An oblique elliptical cylinder has only one particular slicing angle which results in a circle, rather than some other ellipse.

The belt ellipse of an oblique circular cylinder...