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.