There are some Cad related scripts out there that might do this kind of thing. I’m sure otherwise it would be reasonably simple to do something like this with a bit of python.

Just add the vector (y * cos(x * pi / 180), y * sin(x * pi / 180)).

It would be something like

from math import pi, cos, sin

cursor.x += y * cos(x * pi / 180)
cursor.y += y * sin(x * pi / 180)

The * pi / 180 is because you probably want to input degrees, not radians. The cosine gives you the x displacement on a unit circle, the sine gives you the y displacement. This way you point in the right direction. You multiply by the length to go the desired amount of units in that direction. It is just really basic trigonometry.

The main problem I see with this is you’d need some special magic because blender works in a 3d workspace while the mockup only deals with a 2d space.

Is the cursor supposed to move on the X axis or Y axis? Follow the plane of the view like left click placing of the cursor currently does? How about if you wanted to move the cursor on the Z axis? What about rotating on more than one axis?

Lots of non-obvious corner cases to be worked out.

since is CAD drafting, the best way to do this would be to hit 7, 1 or 3 and then 5 on numpad, to enter in ortho mode. Then it should make sense.
watch the video and you’ll get it!

If you compare the two objectively, the current one is actually quicker

Current:

Switch pivot point to active element
Select vertex
E - extrude
X - axis
5 - length
click
Select extruded element
Select vertex for pivot point
R - Rotate
Enter angle
Click

10 Clicks/keys
1 Menu

Proposed:

Select vertex
Shift+S align cursor to selected
Click length
Enter length
Click angle
Enter angle
[axis selection]
Shift+A - add plane
W - merge
Select original vertex
Select new vertex
F - fill

There are easier ways this could be done without no cursor.
When extruding, you should be able to write in the angle, not just the lenght.
When a length is specificated with the numpad, it should lock the length and let you freely select the direction (or type it in)
Or, you could choose to specific the direction and then select the length.

Blender doesn’t actually need much to get good at precise modeling, maybe even making blueprints
I’ve made a proposal on Blenderstorm on what it needs to become that awesome: http://www.blenderstorm.org/blenderstorm/idea/285/

Actually If you have active element set for pivot point(next to viewport shading drop-down) then you don’t need to mess with the cursor. The last element selected is the active element and will be the pivot point.

I would like the ability to set the angle while extruding (and all transformations) too.

But I think it should be implemented differently:

E, G, R, or S
Click and hold MMB+Type angle
The two axis lines(R,G,B/X,Y,Z) that the white line(appears while holding MMB) is between will be the plane that the angle will be on
[maybe have the ability to enter an angle followed by a comma and then another angle so the vector will be 3D]
Then after releasing MMB enter scalar(length,scale,etc.)

This way everything stays the same except you now have the option to enter an angle