Tough to say. When they announced it, I figured that it would be members just because they hardly ever make new f2p stuff.
HOWEVER, I saw a screen cap on Zybez where a moderator was saying that it would be f2p. So I went back to the development diaries and i couldn't find anything that said it was members only. Nor did I find any indication that it was f2p.
So it looks like it may be f2p. We'll have to see when it comes out.