Hi Brian,
If there was to be another 1.6 release, then I imagine it would be called 1.6.10. However, as Martin mentioned in his announcement New releases: Moodle 1.9.4, 1.8.8, 1.7.7 and 1.6.9, "Moodle 1.6.9 and Moodle 1.7.7 mark the last builds that the core team plan to release from those branches (unless someone else volunteers to maintain them) due to the amount of work involved."