Long story short, GCC 6 remains on track and is still in a regression/documentation fixing mode with hope of officially releasing it as GCC 6.1 next month. He mentioned in today's status report, "We're now half-way through our usual period of shaking out regressions before a new release which would be released mid April if we can trust past years experience."
The regression count has been dropping with 67 fewer P1 through P3 regressions in this report. As of today there are 16 P1 regressions left (the highest priority), 82 P2 regressions, 14 P3 regressions, and 106 P4 regressions and 28 P5 regressions of the lowest priority.
GCC 6 is bringing many new compiler features and we'll have more on the features and performance changes with compiler benchmarks as the official GCC 6 release approaches in April.