As Isaac posted
here, UBB.threads v7.7 will require PHP 5.5+; if one requires support for PHP builds prior to PHP5.5 they'll need to install the appropriate outdated version.
New branches on the UBB.threads release tree will be worked on, we will not be maintaining more than one tree of versions (aka, you install UBB.threads 7.6.2 for support on PHP5.4, it will not continue getting new features as we'll be working on UBB.threads 7.7)