TODO update about interpolation

Signed-off-by: martin f. krafft <madduck@madduck.net>
diff --git a/TODO b/TODO
index 31ce28f..78b5046 100644
--- a/TODO
+++ b/TODO
@@ -8,3 +8,6 @@
 - Verbosity options, debugging
 - Add a configuration option to allow a set of classes to be slapped onto
   nodes by default (#5).
+- Think about alternative implementations for Parameter interpolation, as
+  DictPath and RefValue are a bit cumbersome. It works, but it's not exactly
+  intuitive or pretty.