Following scenario: A government would like to destroy Bitcoin. It buys a significant number of ASICs to build up a huge mining farm and carries out a 51% attack.
From my point of view it will not be so easy to buy so many ASICs as once - what do you think?
Another question: Will it be noticed (how?) that somebody buys a big stack of ASICs and/or are we able to identify such a behavior monitoring the network's hashrate?
Such an attack can lead to nothing significant, but an attackers wallet transaction reversal, and also such an attack may result in chain split, where most of the honest nodes will not follow the attackers version of blockchain.