Sorry, forget to mention one crucial thing for the double spend: It only applies to 0-conf+0-fee (actually, low-fee) transactions. Currently, when calling sendrawtransaction your node will accept low-fee transaction into the local mempool but then very likely fail to relay it. This is because other nodes probably won't accept/relay 0-fee transactions. If at the same time a conflicting transaction is sent to the network, it will be fully propagated and at some point arrive on your own node...which will then drop that TX because it already has the 0-fee TX in the local mempool (first seen relay policy). So, your node won't notice that every other node in the network doesn't even know about the original TX and eventually the conflicting TX will be mined.
With sendrawtransaction rejecting low-fee TXs by default, this at least shouldn't happen by accident...for example when a block explorer blindly forwards raw transactions entered into some text field on a web page (that's what happened in the video).
There are still some parts missing here, especially in the UI.