Text on a Shape

Background

SVG has had Text on a path since the beginning. We have been requested to extend this to allow text on a shape. This avoids the need to convert shapes to paths prior to using them with <textPath>.

Typical uses:

Originally, Inkscape drew circles and ellipses using paths, now that Inkscape uses the circle and ellipse elements, people are asking why can't you put text on circles and ellipses?

Requirements

The major requirement for how SVG shapes should be converted to paths has been solved in the discussion of markers on shapes:

... rounded rects start at straight horizontal line of the top left
... rounded rects wind clockwise and include 0 length segments when the rounder corner is 50%
... for ellipses and circles, the path starts at right-most point and consists of 4 arcs going clockwise and each are 90 degrees

Text on a circle, starting at the nominal position.

Text on a circle, with startOffset="75%" and text-anchor="middle".

Text on a circle, with startOffset="50%" and text-anchor="middle", after rotating path 90 degrees.

Text on a rounded rectangle, starting at the nominal position (determined by marker placement rules).

Challenges

How do you place text along the inside of a circle? Would it be better to have a property to specify the side of the path to draw the text?

Text on a circle, with startOffset="50%" and text-anchor="middle", after rotating path 90 degrees and flipping.
What happens if you set startOffset negative?
What happens if you run off the "end" of the path, should you wrap around?
Could startOffset use variable path-width syntax? This would be useful even for normal paths:

Text on a rounded rectangle, using variable path-width syntax to center along top.