Bit of update here!!
As suspected by us, Lumia 950 and Lumia 950 XL need to have their images submitted to WDRT before enabling them for Insider Program. And we have a probable timeline of “next week”, as confirmed by the Program Manager Windows Insider team.
— Jason (@NorthFaceHiker) November 20, 2015
Lumia 950 went on sale (officially) yesterday in US and Lumia 950 XL is supposed to join it soon. Now, in case you are a Windows Insider and want to get new build on your shiny new Lumia 950, it seems you won’t be able to do it as of now. As per Gabe Aul, they need to get support in place for Lumia 950 and Lumia 950 XL to enable them for Insider Previews.
@zeke_again Not yet, we need to get some support in place for 950 & 950XL to enable them for Insider Previews
— Gabriel Aul (@GabeAul) November 20, 2015