Proof of Concept, skipping some specs on Rubinius, also see rspec-support

lib/rspec/support/spec/prevent_load_time_warnings.rb:53
-  it "issues no warnings when the spec files are loaded", :slow do
+  it "issues no warnings when the spec files are loaded", :slow, :unless => (RUBY_PLATFORM == 'java' || (defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx')) do
     expect_no_warnings_from_files_in "spec", "require 'rspec/core'; require 'spec_helper'"
   end

Author: bf4

features/core_standalone.feature

@@ -5,6 +5,8 @@ Feature: Use rspec-core without rspec-mocks or rspec-expectations
   available, but rspec-core can be used just fine without either of those
   gems installed.
 
+  # Rubinius stacktrace includes kernel/loader.rb etc.
+  @unsupported-on-rbx
   Scenario: Use only rspec-core when only it is installed
     Given only rspec-core is installed
       And a file named "core_only_spec.rb" with:

spec/rspec/core/drb_spec.rb

@@ -1,7 +1,7 @@
 require "spec_helper"
 require 'rspec/core/drb'
 
-RSpec.describe RSpec::Core::DRbRunner, :isolated_directory => true, :isolated_home => true, :type => :drb, :unless => RUBY_PLATFORM == 'java' do
+RSpec.describe RSpec::Core::DRbRunner, :isolated_directory => true, :isolated_home => true, :type => :drb, :unless => (RUBY_PLATFORM == 'java' || (defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx')) do
   let(:config) { RSpec::Core::Configuration.new }
   let(:out)    { StringIO.new }
   let(:err)    { StringIO.new }

spec/rspec/core/formatters/documentation_formatter_spec.rb

@@ -78,8 +78,8 @@ def execution_result(values)
 ")
     end
 
-    # The backrace is slightly different on JRuby so we skip there.
-    it 'produces the expected full output', :unless => RUBY_PLATFORM == 'java' do
+    # The backtrace is slightly different on JRuby/Rubinius so we skip there.
+    it 'produces the expected full output', :unless => (RUBY_PLATFORM == 'java' || (defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx')) do
       output = run_example_specs_with_formatter("doc")
       output.gsub!(/ +$/, '') # strip trailing whitespace
 

spec/rspec/core/formatters/progress_formatter_spec.rb

@@ -42,7 +42,7 @@
   end
 
   # The backrace is slightly different on JRuby so we skip there.
-  it 'produces the expected full output', :unless => RUBY_PLATFORM == 'java' do
+  it 'produces the expected full output', :unless => (RUBY_PLATFORM == 'java' || (defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx')) do
     output = run_example_specs_with_formatter("progress")
     output.gsub!(/ +$/, '') # strip trailing whitespace