In TinyMCE, break blockquote by hitting enter like in Gmail

I have set up an open source plugin that sounds like it does what you need to work with the latest version of TinyMCE.

You will need to copy the code to the plugin folder (see https://www.tinymce.com/docs/advanced/creating-a-plugin/ for details )

Demo http://fiddle.tinymce.com/7Qfaab/3

/*
   Original Source: https://github.com/Tauop/tinymce_splitblockquote-plugin/blob/master/tiny_mce/plugins/splitblockquote/editor_plugin_src.js       
   NOTE: Modified by K Scandrett to work with current TinyMCE (~4.6.1)
*/ 

/* @author Patrick Guiran <pguiran@linagora.com>
 * @license GNU GENERAL PUBLIC LICENSE, Version 2
 * @copyright Copyright © 2010, Linagora, Patrick Guiran <pguiran@linagora.com>
 */

tinymce.PluginManager.add('SplitBlockquote', function(ed, url) {
  ed.on('click', function (e) {
    var parts, i, node, bq_node, openTags, closeTags, splitToken;

    if (e.keyCode != 13) {
      return; /* do nothing */
      }

    // get the top-most blockquote parent node
    function getMostTopBlockquote(n, r) {
      var last_bq = null;
      while (n) {
        if (n == r)
          break;
        if (n.nodeName === 'BLOCKQUOTE')
          last_bq = n;
        n = n.parentNode;
      }
      return last_bq;
    };



    function getClose(n, r) {
      // get the htnk "close-tag" of a node
      function getCloseTag(n) {
        if ( n.nodeName === 'FONT' && ed.settings.convert_fonts_to_spans) {
          return "</span>";
        } else {
          return "</" + n.nodeName.toLowerCase() + ">";
        }
      }

      var result = '';
      while (n) {
        if (n == r)
          break;
        result += getCloseTag(n);
        n = n.parentNode;
      }
      return result;
    }

    function getOpen(n, r) {
      // get the html "open-tag" of a node
      function getOpenTag(n) {
        var attr, copy;
        copy = n.cloneNode(false);
        copy.innerHTML = '';
        attr = ed.dom.getOuterHTML( copy )
                 .replace(new RegExp( '<'  + copy.nodeName, "i"), '')
                 .replace(new RegExp( '</' + copy.nodeName + '>', "i" ), '');
        return '<' + copy.nodeName.toLowerCase() + attr;
      };

      var result = '';
      while (n) {
        if (n == r)
          break;
        result = getOpenTag(n) + result;
        n = n.parentNode;
      }
      return result;
    }

    node = ed.selection.getNode();
    bq_node = getMostTopBlockquote(node, ed.getBody());
    if (!bq_node) // we aren't in a blockquote
      return;

    /* Create an unique splitToken */
    splitToken = '_$'+ (new Date()).getTime() + '$_';
    ed.selection.setContent(splitToken, {formar: 'raw'});
    parts = ed.getContent().split(splitToken);

    /* blockquote can handle DOM tree. So we have to close
     * and open DOM element correctly, and not wildly split
     * the editor content. Plus, openTags has to keep all
     * attributes to keep makeup of DOM elements, we split.
     */
    openTags = getOpen(node, bq_node);
    closeTags = getClose(node, bq_node);

    if (ed.settings.convert_fonts_to_spans && openTags != '') {
      /* juste convert </span> to </font>
       * if <font> are converted to <span>
       * as n.nodeName returns "FONT" for <span> node :/
       * @see tinymce.Editor.-_convertFonts() for more information
       */
      (function() {
        var font_count = ( openTags.match(/<font/ig) || [] ).length;
        for (i=0; i<font_count; ++i) {
          start_idx = parts[1].indexOf('</span>');
          if (start_idx != -1) {
            parts[1] = parts[1].substring(0, start_idx)
                     + '</font>'
                     + parts[1].substring(start_idx + 7);
          }
        }
      })();
    }

    /* Update the editor content :
     *  - part[0] : content before the selection, before split
     *  - closeTags : </tag> to close correctly html tags
     *  - </blockquote> : close the blockquote
     *  - <br id='__' /> : <br /> are converted to "<p> </p>". The id 
     *                     is used to change the location of the selection (cursor)
     *  - <blockquote> : open the new blockquote
     *  - openTags : re-open splited DOM nodes correctly
     *  - part[1] : content after the selection, before split
     */
    ed.setContent(   parts[0] + closeTags
                   + "</blockquote><br id=\"__\"><blockquote>"
                   + openTags + parts[1] );

    /* delete empty <p>aragraphe at the end of the first blockquote
     * and at the beginnig at the second blockquote.
     * Delete id attributes to */
    function clean_node(node) {
      var node_html;
      if ( node == null || node.nodeName != 'P' ) {
        return;
      }
      node_html = node.innerHTML.trim();
      if (node_html == '' || node_html == '<br mce_bogus="1">' || node_html == '<br>') {
        ed.dom.remove(node);
      }
    }

    bq_node = ed.getBody().getElementsByTagName('blockquote');
    for ( i = 0; i < bq_node.length; ++i) {
      if ( bq_node[i] == null ) { continue; } /* paranoiac mode */
      clean_node( bq_node[i].firstChild );
      clean_node( bq_node[i].lastChild );
      if ( bq_node[i].innerHTML.trim() === '' ) {
        ed.dom.remove( bq_node[i] );
      }
    }

   /* get the <br id="__"> element and put cursor on it */
    node = ed.dom.get('__');
    node.removeAttribute('id');
    ed.selection.select(node);
    ed.selection.collapse(true);

    /* Don't interpret <ENTER> again, to prevent a new "<p> </p>" to be added */
    return tinymce.dom.Event.cancel(e);
  });
});