UBB.threads v7.6.0 isn't publicly accessible, as it's currently in Alpha Testing; I assume that you meant v7.5.9.
Until PHP7 becomes more widely spread, it's on the back burner, as we're currently working on completely rewriting the overall base code; we've had some internal discussion about various database driver (MySQL/MySQLi/PDO), but it's not a necessity currently with where development is right now (things like default settings for servers of 2016 vs 2000, mobile compatibility, HTML5, Suhosin compatibility [a PHP security module], and numerous other upcoming changes [which can be viewed here and at UBBDev] are what we've been attempting to tackle since the last release [7.5.9]).
We plan to look into PHP7 compatibility at a later junction however, but it'd be a release after v7.6.0 is out the door.
