There actually have been huge reliability issues with adding more gears into the same space as previous units, everything has to be smaller to fit. We are building GM/Ford 10 speeds and ZF 8 Speeds like crazy. The Ford/GM units fail anywhere from 70-100k most ZF 8 speeds are in the 100-120k mile range. Also seeing huge early failure issues on the Toyota 8 Speeds.Thr newer 8-speed or 9-speed automatic is nothing special but squeezes in 2 or 3 extra gears in there. The reliability issue has nothing to do with the concept of adding additional gears. If Toyota can do it, everybody else can do it too if they’re willing.
Cylinder deactivation on the other hand is a totally different story.
Mazda has an 8 speed FWD/AWD transmission that they keep updating the patents on throughout the years. Whether it will be produced or not is another story.