I think you’re right on, but good luck with provable timestamps. You’re trying to coordinate and validate a measurement which in itself denies the reality of space time physics at least subtly. Time precision across space is hard enough, but adding bad actors and gravitational time dilation into the equation means... well I wouldn’t want that to keep track of my assets.
On the bright side, if approaching the speed of light would give you a viable attack on the bitcoin blockchain I'm sure our space propulsion technology would transform overnight!
The nice thing about relativity (special and general) is that all of the weird seeming-paradoxes 'sort themselves out' eventually. In particular, whilst we lose a total ordering for events, we never lose causality; i.e. two events can only appear in a different order to different observers if those two events are independent (no information has travelled between them, and hence neither one can influence the other).
