The new gem appears to have installed without problems, thank you! Will rubygems pick it up when the version number is next bumped?

PS C:\test-gem> gem environment
RubyGems Environment:
  - RUBYGEMS VERSION: 2.2.5
  - RUBY VERSION: 2.1.8 (2015-12-16 level 440) [x64-mingw32]
  - INSTALLATION DIRECTORY: C:/Ruby21-x64/lib/ruby/gems/2.1.0
  - RUBY EXECUTABLE: C:/Ruby21-x64/bin/ruby.exe
  - EXECUTABLE DIRECTORY: C:/Ruby21-x64/bin
  - SPEC CACHE DIRECTORY: C:/Users/passp/.gem/specs
  - RUBYGEMS PLATFORMS:
    - ruby
    - x64-mingw32
  - GEM PATHS:
     - C:/Ruby21-x64/lib/ruby/gems/2.1.0
     - C:/Users/passp/.gem/ruby/2.1.0
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/
  - SHELL PATH:
     - C:\DevKit-mingw64-64-4.7.2-20130224-1432\bin
     - C:\DevKit-mingw64-64-4.7.2-20130224-1432\mingw\bin
     - C:\Ruby21-x64\bin
     - C:\WINDOWS\system32
     - C:\WINDOWS
     - C:\WINDOWS\System32\Wbem
     - C:\WINDOWS\System32\WindowsPowerShell\v1.0\
     - C:\Program Files\SysinternalsSuite
PS C:\test-gem> gem install --local --verbose io-console
C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/io-console-0.4.6/console.c
C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/io-console-0.4.6/depend
C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/io-console-0.4.6/extconf.rb
C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/io-console-0.4.6/lib/console/size.rb
C:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/io-console-0.4.6/win32_vk.inc
Building native extensions.  This could take a while...
C:/Ruby21-x64/bin/ruby.exe extconf.rb
checking for rb_funcallv()... yes
checking for rb_sym2str()... no
creating Makefile
make "DESTDIR=" clean
make "DESTDIR="
generating console-x64-mingw32.def
compiling console.c
linking shared-object io/console.so
make "DESTDIR=" install
/usr/bin/install -c -m 0755 console.so ./.gem.20160419-3528-1r28flb/io
installing default console libraries

Successfully installed io-console-0.4.6
Parsing documentation for io-console-0.4.6
Parsing sources...
100% [ 8/ 8]  lib/io/console/size.rb
Installing ri documentation for io-console-0.4.6
Done installing documentation for io-console after 0 seconds
1 gem installed
PS C:\test-gem>

Note:

rubygems prevents to ship to default gem now.

see. https://.com/rubygems/rubygems.org/pull/1221