Update issue on IRI to #15.

Author: gkellogg

spec/index.html

@@ -492,9 +492,13 @@ <h3>IRIs</h3>
       of [[!RFC3987]]. Further normalization MUST NOT be performed when
       comparing IRIs for equality.</p>
 
-      <p class="issue" data-number="4">
-        [[RFC3987]] never made it past the Proposed Standard phase
-        and should not be normatively cited.
+      <p class="issue" data-number="15">
+        A future version of this specification may use [[?URL]],
+        as [[?RFC3987]] is an abbandoned specification.
+        This would include retaining mos of the `IRI`-based nomenclature, but
+        defining in terms of
+        <a data-cite="URL#absolute-url-with-fragment-string">absolute-URL with fragment string</a>
+        and <a data-cite="?URL#relative-url-string">relative-URL string</a>.
       </p>
 
     <div class="note" id="note-iris">