Registered jacks should be called that only when used for specific telephone signals. The connectors for RJ11 and RJ45 are called
modular connectors.
Jacks made especially for RJ45 also contain transformers, which would mess up TTL level signals.
I like modular connctors. The sockets have small footprint on the PCB and the cables are inexpensive, easy to do yourself and the plugs are short so there is no stiff part sticking out.
I find it difficult to find one that is not very high, though. I have not found a socket that goes inside a cutout in the PCB like some mini/micro-USB sockets.
The Ultimate Hacking Keyboard uses a 4P4C socket that is relatively small but I have not found any like it.
4P4C is enough for I2C, V+ and GND.
I have looked at 6P6C because it would also be able to carry a pulse width-modulated current for the Caps Lock LED, giving the builder a choice between the LED in the Caps Lock key itself on the left side and a dedicated LED area on the right.
The "VE.A" keyboard uses 7-pin SATA connectors. The plugs are small. The sockets are also small while still being through-hole that can be soldered by hand, but the cables are very stiff and were never designed for many reinsertions.
... makes it harder to make slim cases.
"Floating keys" looks like crap anyway...