Import/export/backup saved world in Minecraft Windows 10 Beta?

Hi Aprianto,

Thank you for using Windows 10.

I would like to inform you that for issues related to gaming, we have a dedicated support.
Please post your query in the following forums for better assistance on this issue.
http://forums.xbox.com/xbox_forums/xbox_support/xbox_on_windows_support/default.aspx 

Hope it helps. If you have any other questions, please do not hesitate to reply. We will be glad to assist.

Here you go:

Q. Where does Minecraft Windows 10 edition save the game worlds?

A. Unlike the regular Minecraft which saves the worlds to location %USERPROFILE%\AppData\Roaming\.minecraft\saves\, the Windows 10 edition saves the worlds to %USERPROFILE%\AppData\Local\Packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\
LocalState\games\com.mojang\minecraftWorlds. The worlds save in different formats so you cannot just copy worlds from the java based version to the Windows 10 version.

source:

Supersite for Windows

this file worked for "C:\Users\Your PC Name\AppData\Local\Packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\LocalState\games\com.mojang\minecraftWorlds"