When trying to enter a debug world's End dimension you normally get the credits playing. How ever if you enter the portal and crash the game befor the credits start (i.e. with Alt+F4) you will after reloging actually be in theEnd. When there you should be able to see
a boss bar and EndCrystals (no Obsidian pillars)

Way to reproduce (in a nutshell)

1.create a debug world by creating a new world and holding Shift whist selecting a world type (if you do Debug mode shall pop up after customised)
2.set your self to gamemode 1 (/gamemode1)
3.Go to the EndPotal block (can take a while but you'll manage :])
4.Position yourself over the portal whlist flying. Than fall in to the portal and press Alt+F4 when inside (befor the credits screen)