for the un-enlightened amongst us, can someone summarize what an "alert key" would allow the holder to do? and what implications that would have
A holder of the alert key can send alert messages that will appear at the top of Bitcoin Core. All it really does now is to inform people that there is a situation with the Bitcoin network and that they should check Bitcoin.org for more information.
It could be used to cause a panic e.g. someone sends out an alert saying that an upgrade is necessary even though such an upgrade is not necessary. However, other alerts can cancel out previous alerts and one alert message type displays a static "Alert Key Compromised" which cannot be canceled and does not allow any further alerts signed with the alert key.