So today, May First, My Friends and I were exploring the end, trying to get to new islands. Each time we found a new one, the world-guard border would keep us from exploring more. I believe the border should be expanded, if possible.
I believe it was said that the end is only in a sort-of test phase right now and will end up being rolled out in full (much more expansive) relatively soon. This is based off of conversations when it first opened up for the dragon fight, so no accuracy is guaranteed.
As much as I want the end border to open, I worry about it causing massive lag because you'd have people loading chunks in every dimension.