You can easily import any zip and turn it into your site. Just drop a zip onto the drop-area and you can edit it soon afterwards.
When you import an existing site, it will replace existing files in the site with the data from the zip. Importing sites will not delete files in your site.
There is a WordPress plugin called WordPress to Jekyll exporter that allows you to turn your WordPress into a Jekyll site.
Whatever comes out of this plugin, you can host with Soverin.
At some point we may offer direct import from a WordPress XML file, but this isn't on the roadmap yet.