Top level DSL is make the default (for now).

lib/rake/application.rb

@@ -371,7 +371,7 @@ def standard_rake_options
         ],
         ['--top-level-dsl', '-X', "Put Rake DSL commands in the top level scope.",
           lambda { |value|
-            Rake::DSL.include_in_top_scope
+            options.top_level_dsl = value
           }
         ],
         ['--trace', '-t', "Turn on invoke/execute tracing, enable full backtrace.",
@@ -417,6 +417,8 @@ def handle_options
         opts.environment('RAKEOPT')
       end.parse!
 
+      Rake::DSL.include_in_top_scope if options.top_level_dsl
+
       # If class namespaces are requested, set the global options
       # according to the values in the options structure.
       if options.classic_namespace