For some days i am looking for showcase theme preview plugin in wordpress.org for showing my future themes Finally i found WordPress Theme Showcase Plugin in wordpress.org , but it was 8 years old and not updated. So i just modify it a little to meet my needs. The plugin is simple and just like my expectation so i add javascript to make it work in post , page and category.
Beside using shortcode [theme_showcase] , you can use Theme Preview widget on sidebar / footer to choose theme preview which you want
I upload it to wordpress.org so it’s usefull for anybody and can be modified as they need. This plugin is usefull for wordpress theme developer showcase their simple themes.
You can see the demo here : http://reviews.wpamanuke.com/theme-preview/