I would like to see the introduction of transmission gates. transmission gates are a BIDIRECTIONAL gate used in many applications such as multiplexers and perform very simular to a valve on a pipe. When a signal is provided to the gate junction, it allows signals to traverse the gate in either direction. Some information may be gathered here: https://www.maximintegrated.com/en/app-notes/index.mvp/id/4243

What does this help with? A massive reduction in circuit sizes when arrays of the same thing over and over are built. It can be used in many applications but one large scale example could be say the construction of more compact one time programmable ROM, or complex multiplexers, passive decoders, etc.

Edited: Link fix.

Completely agree. In one of my planning build there are some interconnection parts where most of wires need to be bidirectional and reconfigurable with redstone signals independently and can be fit into an IC gate at the same time. The transmission gates fits that requirement pretty well.