emphasizing that we are not advocating a replacement for MathML

Emphasize that we don't advocate combining Unicode-base math formatting with MathML, as pointed out by @pkra in #3.

subsuper-proposal.tex

@@ -123,11 +123,13 @@ \section{Summary}
 of the additions, excluding the vast majority of Unicode characters
 from consideration.
 
-While it is probably not practical to encode the full range of mathematical
-notations in Unicode---MathML and similar will always be useful---subscripts
-and superscripts are low-hanging fruit that would be tremendously
-beneficial to computer programming in technical fields and are already
-partially present in Unicode. We respectfully urge you to expand the
+It is not practical to encode the full range of mathematical
+notations in Unicode; MathML and similar will always be useful,
+and generally should not be combined with Unicode-based formatting.
+However, in programming contexts, where non-Unicode math formatting
+is unavailable, increasing the set of available subscripts
+and superscripts is a ``low-hanging fruit'' that would be tremendously
+beneficial in technical fields. We respectfully urge you to expand the
 set of mathematical subscripts and superscripts, and especially to
 eliminate frustrating omissions from the Latin and Greek alphabets.