That's pretty much what we already have, isn't it?

True Time™ is determined by essentially averaging dozens of atomic clocks from laboratories all over the world. It doesn't really get any more "community-maintained" and "democratized" than that!

Put it on the clockchain

The article, and this comment, makes me wonder what impact a coordinated attack on the root time-keeping mechanisms might have. It seems like there's a fair bit of redundancy / consensus, but what systems would fail? On what timeline? How would they recover?

It's probably possible to calibrate your clock using a clear night sky and a modern cell phone camera. I bet second accuracy isn't an absurd expectation. Now it'd probably take an unreasonable amount of time to calibrate...

Bring out the water jug with a hole in it

we're not, it's run by the government