@senso: This is the solution I actually needed, thanks a lot! I see they can be daisy chained too. Skimmed this briefly due to a dayjob, don't understand it well at the moment, will dig into it tomorrow to get to the core. Thank you again!
One question: is N key rollover possible with these? (y/n suffices, or keyword I should search for if counterintuitive)
What do you mean by
... connect each individual key of a keyboard to an input in ATMega
Uh oh... I wrote that, didn't I...
It should be "how do I increase a physical number of inputs of an ATMega, so I can physically connect each of the switches to those inputs". Using a muxer/demuxer is the answer, it seems.
What I wrote before is an ugly leftover from the thought process that led me here.
It referred to a hypothetical situation in which the amount of outputs from all available switches equaled the amount of inputs available on the ATMega. In that situation, I would simply wire every switch to every pin and handle it on the ATMega side, fast and ugly. Then I hypothesized about a situation when the amount of outputs is bigger than the amount of inputs, and how do I wire it up then.
And this sentence popped up as a derivative of this process, and my lack of knowledge and understanding
Using I2C in this situation is a wrong choice, but the only one I knew (aside from soldering different resistors to each switch and grabbing the resulting voltages on analog pins, but that's fugly as hell and has its own issues).
I should have posed the question differently.
EDIT:
I'll be back to the subject of I2C when I'll be wiring up LEDs.