As @Xtreix mentions, this is a topic that has been discussed numerous times.
We'd like to do it, but it's not possible to do in a proper way with the supported hardware. Additionally, even if it was, the IMEI isn't the only identifier, so it wouldn't be a complete approach.
As threads on these topics tend to lead to arguments and a ton of misinformation, I will be locking it. People can refer to official responses in existing threads for information on this topic.