When the YouTube Live Streaming feature was launched you had to have 10,000 subscribers to use it, this was then reduced to 1,000.
Now it would appear that YouTube has removed the subscriber requirement for YouTube Live Streaming and now anyone can use it.
The YouTube Live Streaming feature is now available to all uses of the YouTube app and you no longer have to have a certain amount of subscribers to use it.
You will need the latest version of the YouTube app to use the live streamign feature and you can find out more details about the app over at Google.
Source Android Police