Who really cares about some “empty block” attack? No one, really. Who would want to do this? Nobody, really. Shutting down 70-80% of mining/block creation capacity? Now, that’s something a large and growing number of people would care about. Replacing that capacity would be next to impossible in any short amount of time (leaving aside costs) and recovering from the annihilation of “trust” in crypto would be essentially next to impossible.
Of course, that’s not really the issue. Who would have the motive for doing such a thing?
If things continue to develop and crypto becomes more and more mainstream in western liberal democracies and is found in larger amounts in more corporate treasuries (Tesla, Twitter, Microstrategy, etc.) and large western banks create and sell derivatives and indexes and sell custody and all other kinds of asset/monetary services, well, they are extraordinarily vulnerable. So much so, the effect on the trust of the institutions underpinning the dollar reserve system could be at least shaken if not entirely undermined.
Cui bono? Who would benefit from the loss of confidence in these financial institutions and systems of governance? Well, the list is in some ways fairly long, but generally: non-democratic oligarchies, terrorist groups, kleptocracies, and totalitarian governments of all kinds that currently chafe or are restrained under the current system.
China (on its own territory) has 66+% of hashing for BTC and as large or larger for other major coins. Another ~20% is mined in Mongolia by Chinese-owned operations. Let’s be clear, China has the capability and the motive to shut these down entirely at some point when doing so would have the effect of destabilizing western financial institutions and destroying trust in the dollar reserve system. And those intentions are well-sketched out in their open enmity to the dollar reserve system and their current projects (Belt-and-Road, Digital Renminbi, etc.) to undermine and/or escape it.
A country that can imprison and re-program a large religious-ethnic group (Uighurs), suppress the culture and language of another (Tibet), ignore a treaty they signed and takeover the government of a territory and start to systematically imprison all opposition (Hong Kong), build a string of artificial islands in the South China sea and declare those Chinese territory where international treaties have already settled claims for other countries… that country does not care terribly much about any repercussions of closing down all crypto mining under its control.
And there would be no effect on Chinese citizens. As of November 2019, it is illegal for any Chinese citizen at home or abroad to transact crypto of any kind or even have an account on exchange that offers crypto-trading. And the economic importance of mining rigs and crypto mining is tiny.
And timing is everything. The efforts by China to circumvent the dollar economy are accelerating and with the arrival of the DRMB, they will speed up even more. Crypto has a good shot at being the Achilles Heal of the Western Liberal Democratic project.
So never mind “empty block attacks” or any other such nonsense. Keep your eye on the man behind the curtain.
