diff --git a/otf2.spec b/otf2.spec
index f3e38aa..1a49678 100644
--- a/otf2.spec
+++ b/otf2.spec
@@ -8,6 +8,12 @@
 %bcond_without python2
 %endif
 
+# Note that we could package and use sionlib, which can improve otf2
+# scalability, but it's not clear how worthwhile that might be for the
+# packaging.  A maintainer says it will help around 8000 processes,
+# and maybe fewer, and that building with it still allows reading and
+# writing of non-sionlib traces.
+
 Name:           otf2
 Version:        2.2
 Release:        10%{?dist}