As to me, RepRap describes its protocol clear enough (see link above). There are variations yet not so significant to make it impossible to implement. This is first. Second, when you are saying that "the problem is "Making sure that the other side understands what you mean"." -- what it has to do with USB, serial comm, WiFi, BLuetooth, Ehtenrnet etc? It still down to the fact that one piece of software cannot (and in our case, as it is clearly seen from the discussion, doesn't want to either), understand another piece of software. That's it.
Based on the problem as you've described it, you may and shall have it in each end very place where you want to send data between two separated entities. If I speak German and you speak English it is absolutely irrelevant what type of connection were are going to use - usb, phone, or written letters. We won't understand each other. So no need to blame "horrible sheet of paper" if a reader cannot understand the writer in this case.
"Horrible" - it is not any quantitative explanation, sorry. Again, there are software products which do support it and their vendors and users don't find it "horrible". USB , serial, or WiFi - are all legitimate carriers layers to send bits over at discussable data rates. There is nothing horrible about any of them. The horrible part starts when software comes in play.
And here is the major point: "our own printers". Precisely! You see, if Cura will position itself as piece of software that supports some specific "our own printers" - then it would be absolutely fine to say "our printers don't have that and our users don't need that either". Anybody who needs something different shall use something different, too - including software. Many vendors, especially printer vendors, do exactly this.
But 90% of CURA's popularity is a result of it's claimed universality and being "best 3D printer software" in a market - plus, certainly, because like those abovementioned "cheap Chinese printers", - it is cheap, too. And somewhere here the failure starts: it is very difficult to claim that you are "universally best" and be at the same time "software for our own printers". And then describe anything that interferes that claim as "horrible thing", including USB 🙂
No matter what, I understood, that there no any plans to include support for low latency wired printer control for your own printers, hence for CURA, too. At least this part is very clear, thanks!