Are floors 76-100 still untouched? At the end of the Aincrad arc, Kirito faced Skull Reaper (boss of the floor) and found out that the Guild Master of the Knights of the Blood was the GM himself. After beating him, Aincrad was destroyed and floors 76-100 were still untouched. 

At the end of the Fairy Dance arc, Kirito restores Aincrad so the people can explore it again.



I waiting for the story about floors 76-100, as well as the Ruby Palace (100th floor), but there has been nothing so far. Now that Kirito has begun exploring GGO (Gun Gale Online), are floors 76-100 still untouched?
Still untouched in canon.  In the non-canon games Infinity Moment/Hollow Fragment, Kirito and the others had to continue through the upper floors and the Ruby Palace.

It was established within canon that the floors of New Aincrad are being released 10 floors at a time.  The Mother's Rosario story arc begins with the update that opened floors 21-30 to begin clearing, notable because Kirito and Asuna wanted to reclaim their cabin on floor 22.  Since nothing has been said beyond Mother's Rosario, it is safe to say the upper floors still have not been released.