TL;DR
Add combinator functionality that incorporates the "case" style logic of the display unit.What?
Unfortunately, the display is one-way - you can program it to do useful stuff, but it has no output signal. If the display had output terminals (broadcasting whatever is being displayed), you could pretty much eliminate deciders. Or you could create a new combinator that does all the stuff the display's logic does, and greatly simply the display unit to just display the first signal it receives, sort of the opposite of a constant combinator.Why?
I love the display unit. Not only can you make digital displays out of it, but it internally uses the conditional structure that I think is most painfully missing in factorio - the case ladder. At present, just doing a simple if-then-else requires two combinators. A display can do that, and a heck of a lot more.With a case combinator, doing logical operations becomes much more "logical". Sure, it's fun (for a while) to construct logic gates out of combinators - but it's also messy as hell on the map, and most combinator constructs of any complexity are more or less write-only. Good luck figuring out someone else's combinator logic, or even your own if you didn't make notes!
A new combinator would be OK, but I think just having the display able to send signals is better. Not only do you get high-quality logic, but you get a pretty little symbol on the ground that gives you the status of that logic. How cool is that?
