Alternatives to an RFID reader
Not the way to do it, but a way...

The RF side is the difficult (as in most variable) part. One option would be to make use of the size of the luggage and embed a "frame antenna" into it - say, 7 turns of copper wire round the entire suitcase. (Convincing manufacturers to embed this into the lining doesn't matter at this stage!)

With the suitcases upright on a conveyor belt, a similar coil beside the conveyor should pick them up at a decent range, maybe up to the size of the suitcase. (With range = size of coil, it's more like inductive coupling than RFID; are there any explicit rules against that? :-)

Spend an afternoon making up a pair of coils, choose a capacitor to resonate them BELOW the AM band (Medium Wave in Europe) - maybe just above the top of Long Wave (280kHz) or even lower like 100-150kHz. Check the regulatory aspects first!

Drive one from a signal generator and see if you can get say 1V or more from the other. If so, you can drive a Joule Thief from it, and wake up a low power CPU like the TI MSP430 to send a message.

Starting with big coils gives you an easier job of getting power across. And if you need example circuits, refer to an electronics handbook from the 1920s!

The best way to signal would be for the transmitter to detect a receiver's presence by noticing a change in load impedance when a receiver is nearby (again you can test that with just the resonant coils and a sig gen) - then the receiver's MCU can disrupt that in some way : perhaps switching in a load, or another capacitance to tune the coil off frequency. 

Once the basic link works, the rest should be easy.