I really like the new ISC with the dual input/output ports.
A natural evolution of this would be a couple ideas:
Improved (Mk2) - The top output port can be set to allow only a specific item (as well as "ANY"), while the bottom output port is hard-locked to "ANY". If the top belt becomes full, then the filtered item would egress via the "ANY" port. It would not choose the lower port if it's just a slow belt causing queuing, only if the belt was full and stopped. Construction costs would be similar to the base model, but add some Quickwire and Circuit Boards for the filtering intelligence
Advanced (Mk3) - This version goes one step farther. First, each port can be set to be either input or output. In addition, each output port can have an item filter applied to it, including "ANY", that uses the same logic as the Mk2 version. Construction costs are similar to the Improved version, but adds a Computer instead of circuit boards for the additional required smarts, plus some Motors to support the internal mechanics.