A friend asked me about this and I couldn't come up with anything. To create an internal single path that is equidistant from the edges.
Trying to find a plugin or tool and not have to do it manually.

There is no other way I know of than the manual one.

Even reversing the problem, using a single path to generate a stroke with a pen shape, that looks as in that image, has only a few hints.
Gerrit Noordzij's book The stroke is suggested by typographers.
http://westspacejournal.org.au/article/winter-2013/our-masthead/

Yet only kalliculator can produce something similar I know of.

For making single line fonts, here are some links mentioned:
http://www.inkscapeforum.com/viewtopic.php?f=22&t=16498#p60905
Here are links presented to sites with single line fonts.


Going back to the original problem.
You have a shape/character made up of strokes, yet for "centerlines" (or heartlines, as written in the mentioned book) you would need at least to know where each stroke's boundaries are at.
Like, on the bottom part, where the rounded stroke enters the stem, any automation would produce a forced result.

Thinking for another aproach, what if the letter was carved into stone, engraved at the same angle. in every part of the contour.
More or less, the line you are searching for would be the deepest part of the carve.
But again, intersections are the problematic part, to give a geometrical construction for -intersecting conic surfaces-.

In that manner, you can use filter effects to generate a fake 3D shading, and trace it for the centerline, but that would be inaccurate at the mentioned intersections.
So is the dynamic offsetting, due to extrapolation of the core is not dealt with.
Here is a bit related topic too.

i remember asking that very same question on Gimpchat

they said the same as Lazur.... its not possible

Thank you very much for the very detailed reply!
That's exactly what I needed to know.

Cheers