So, I haven't got a chance to even try this out yet. but I heard Realm is coming back, I think I hear it's called Realm Re-Awakening Mistwalkers?
Is there a beta I can join or is it still in development?
The Realm Reawakening and Mistwalkers are entirely separate things. The former is the project Stephen began that hasn't been finished yet, and we've no idea when or if it will be. It will be a 'spiritual successor' to it.. meaning new but retaining the Realm feel. Countless topics here lay that out in far more detail.
Mistwalkers is one of two private servers of the old game, but with active development and active changes/improvements. The above link is where you ask for an invite, but I'll bring this post to the attention of the admin.