Dirty hack to emulate visual-block mode using multi cursor feature.

Readme.md

Limitation

• You only can extend selection area for up/down direction.
• When escaped from visual-mode, multi-cursor not cleared.

init.coffee

class VimVisualBlock
  constructor: ->
    atom.commands.add 'atom-text-editor',
      'user:visual-blockwise-j': (event) => @blockOperation(event, 'j')
      'user:visual-blockwise-k': (event) => @blockOperation(event, 'k')

  getVimService: ->
    @vimService ?= atom.packages
      .getActivePackage('vim-mode')
      .mainModule.provideVimMode()

  isVisualBlockMode: (editor) ->
    {mode, submode} = @getVimService().getEditorState(editor)
    (mode is 'visual') and (submode is 'blockwise')

  blockOperation: (event, direction) ->
    editor = atom.workspace.getActiveTextEditor()
    if @isVisualBlockMode editor
      switch direction
        when 'j' then editor.addSelectionBelow()
        when 'k' then editor.addSelectionAbove()
    else
      event.abortKeyBinding()

new VimVisualBlock()

keymap.cson

'atom-text-editor.vim-mode.visual-mode':
  'j':      'user:visual-blockwise-j'
  'k':      'user:visual-blockwise-k'