If I create a world (current seed -2125654492) and immediately go into the nether by creating a portal in creative, the nether roof generates with normal biome specific blocks instead of bedrock.  In the initial test, I noticed the overworld had dirt or some other blocks as the bottom of the world.  I wasn't able to recreate that, and I deleted that world.  

My steps are as follows:

1. Create the world (I used that seed number) - allow cheats, but start in survival with chest
2. immediately, I changed into spectator and gave effect of night vision for 5000 @ 255
3. Then, I changed into creative and gave myself obsidian and flint/steel
4. create 3/5 portal and go into nether
5. go back in to spectator
6. go to roof - It's all biome blocks not bedrock

I thought that was a change or something but couldn't find anything in the release notes.  If I deviate from those steps, it generates properly.

I haven't experimented much with steps or order.

Hope this is helpful.  I'm happy to send world files if you need.  I'll attach screenshots.  I'm keeping this world!!!