What kind of output do you expect from a serial port device at boot time?
Nothing.
Homebrew IR receivers connected to a serial port don't report themselves to the system so it's not possible to detect if they are connected or not.
Loading serial_ir will always succeed, whether you have a receiver connected or not. But of course, if nothing is connected you won't get anything from ir-keytable -t or ir-ctl -r. Just test it for yourself - either with serial_ir on a x86 PC or with gpio-ir-receiver on RPi.
so long,
Hias