One unmentioned issue is that RFID is also not universal. In that, each country has it's own part of the EM spectrum regulated for RFID. And most of these bands

One unmentioned issue is that RFID is also not universal. In that, each country has it's own part of the EM spectrum regulated for RFID. And most of these bands don't overlap. So you need one tag for the US, one for the EU, one for Japan, etc.