Once you've increased the width of these interword spaces to their
maximum, all the characters (and these increased spaces) should be
justified using interletter spacing, and this extra interletter
spacing should be applied as well between the dots of the ellipsis
(showing that they are effectively 3 separate characters and not just
one with a fixed distance between dots).
You are right that tracking and glyph scaling exist, but how exactly
they should be applied to a 3- or 4-dot ellipsis is likely a matter of
font design and typographic style. What you write isn't unreasonable,
but I don't buy it as an absolute prescription. (If it were one,
that'd be an argument against a single-glyph ellipsis.)
Actually, not even that is clear. If there were only tracking, that'd be
an argument against single-glyph ellipses, but glyph scaling can to some
extent take care of them. The best argument against them might be the
lack of good arguments for them ... After all there are many punctuation
clusters, as you pointed out earlier, and it's not like optimal kerning
and tracking behavior is determined exclusively by a glyph cluster's
semantic decomposability.
Stephan