Hi Lars,
I'm not sure i agree with you. The interword space that is relevant
is located between the base line and the x-height line in a font.
I'm not disturbed by fonts like baskerville where the sequence
<period><space><J> leaves a correct space between the point and the
vertical stem of the J, although its tail almost goes to the left of
the vertical of the point.
Side-bearings are adjusted for the typical case where a cap is
followed by a lowercase letter, and lc are inside a word between two
other lc letters. What I'd need is super metrics with kerns to the
left/right-word boundary in order to adapt the side-bearings to that
situation, i even dream of <boundary line> characters allowing kerns
for optical justification. Plus cap-cap kerns fot all-caps words, +...
Not much related to latex2e*++, eh?
Thierry Bouche, Grenoble.