Propane technology has matured and stabilised; a 2019 propane tank is no better than a 2009 propane tank, it'll be the same size, supply the same amount of energy, and have the same connectors. A 2029 propane tank will, in all likelihood, be the same.
The same cannot be said of EV battery technology.
So why the Tesla demo video? According to [1] just doing the demo entitled them to $90 million of Californian "ZEV credits", and they never believed in or planned to roll out the technology.
[1] https://www.quora.com/Whatever-happened-to-Tesla-battery-swa... apologies for the Quora link