TL;DR
Allow using the same fluid network segement with multiple fluids (only one at a time though) without having to remove/place entities.What?
I would like to be able to have sources for multiple different fluids and consumers attached to the same fluid network. Sources and consumers would be separated by pumps wich would be circuit-controlled. There still could be only one fluid type in each segment of the network at any given time. Pumps would not activate when doing so would lead to fluid mixing. But shutting off all connected pumps and activating one pump connected to a fluid source would make the connected fluid network segment change fluid assignment to whatever fluid the pump provides.It would be okay if remaining fluid in a fully disconnected (all pumps are off) network segment would just vanish when activating a pump providing another fluid. But having to empty a fluid network segment myself would also be okay.
Why?
Vanilla would profit by beeing able to use the same setup for making solid fuel from all three suitable fluids (would still have to change recipes by hand or use a mod for that).But the real benefit would be for the heavily modded game where we could build flexible chemical factory blocks wich could automatically switch recipes as needed (recipe-switching by circuit network is available as a mod already, it is the new fluid-mixing-prevention that makes it useless for anything wich would require switching of input or output fluids).