Wordpress Exports to Jekyll. Fill a folder /xml/ with Wordpress exports and generate a folder /output with jekyll ready post files.

index.js

var fs = require('fs');
var _ = require('lodash');
var moment = require('moment');
var parseXML = require('xml2js').parseString;

var existing = [ /* list of your current _post/* filenames, make sure all end in .html */ ] 
var blacklist = [ /* list of files to exclude from output */ ];

function readFiles( dirname, onFileContent, onError ) {
    fs.readdir(dirname, function( error, filenames ) {
        filenames.forEach(function( filename ) {
            fs.readFile( dirname + filename, 'utf-8', function( error, content ) {
                if ( error ) {
                    onError( error );
                } else {
                    onFileContent( filename, content );
                }                
            });
        });
    });
}

function generateFrontmatter( post ) {
    var frontmatter = '';
    var category = _.get(post, 'category[0].$.nicename' );
    var excerpt = _.get(post, '["excerpt:encoded"][0]');
    var title = post.title[0].replace(/["]/g, '\\"');

    frontmatter += '---\n';
    frontmatter += 'layout: post\n';
    frontmatter += 'title: "' + title +'"\n';
    
    if ( excerpt ) {
        var clean = excerpt.replace(/["]/g, '\\"');
        frontmatter += 'description: "' + clean + '"\n';
    }

    if ( category && category !== 'news' && category !== 'blog' ) {
        frontmatter += 'category: ' + category +'\n';
    }     

    frontmatter += '---\n\n'

    return frontmatter;
}

readFiles('./xml/', function( file, content ) {
    parseXML(content, function( error, result ) {
        var posts = _.get(result, 'rss.channel[0].item');
        var organized = {};

        if ( posts && Array.isArray( posts ) ) {

            posts.forEach(function( post ) {
                var type = post['wp:post_type'][0];

                if ( type !== 'attachment' && type !== 'nav_menu_item' ||
                    ( type === 'page' && post['content:encoded'][0] )
                ) {
                    var date = moment( post['wp:post_date'][0] || post.pubDate[0] )

                    var unix = date.unix();
                    var filename = date.format('YYYY-MM-DD');

                    filename += '-' + post['wp:post_name'][0] + '.html';

                    if ( existing.indexOf(filename) === -1 && blacklist.indexOf(filename) === -1 && post['wp:status'][0] === 'publish' ) {                                           
                        organized[unix] = {
                            filename: filename,
                            title: post.title[0],
                            content: post['content:encoded'][0],
                            frontMatter: generateFrontmatter( post )                            
                        }
                    }            
                }
              ;
            });

            for ( var i in organized ) {
                var post = organized[i];

                var finalContent = post.frontMatter + post.content;

                fs.writeFileSync('output/' + post.filename, finalContent);
            }
        }
    });
}, console.error);

package.json

{
  "name": "post-archives",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "lodash": "^4.17.4",
    "moment": "^2.19.1",
    "xml2js": "^0.4.19"
  }
}