I think there should be a way to reverse the way pipe flows by either using what we currently have, (using RPEL and giving it electronic values) or by making a sort of powered pipe that reverses according to the type of silicone sparking it. It would be useful in many factory saves that are mixing things in order to cause a reaction, you would also be able to make a few new type of saves if you have several powered pipes being used. including fountains, water treatment plants, etc. I have been thinking we needed something like this for a while and I think it would be very useful to have.
Well, it'd certainly make pipe different from portal at least.
...However, I'm still trying to imagine how pipe that is already difficult to set up for one-way transit would be useful for two-way transit? XD And don't forget that pipes which diverge or converge might be weird, too.