Linux Mint has once again, announced, that they will soon release a beta, but have included no details, no source code, and no developer downloads.
Honestly, if you visit their GitHub, for example, at the time of this posting, there is very little to do with the next release being public (there is some, but not enough for a whole OS).
I have always disliked how Mint Linux seems so scetchy and closed, about their releases.