The article mentions Ethereum several times, so here are some Ethereum-specific updates for 2021. It's still a work in progress but some progress has been made.
1) Scalability
For now, the big advance is a layer-2 approach called "rollups," several of which are in production already and able to handle several thousand transactions per second. Zkrollups do that without compromising security assumptions at all, but aren't quite to the point of handling arbitrary smart contracts. Optimistic rollups can handle arbitrary contracts but require a delay for funds withdrawal since they rely on fraud proofs.
About a year from now, data sharding will multiply rollup capacity by 23X. [1]
2) Key management
Vitalik agrees on this point and advocates social recovery wallets, where your friends and/or service providers give you some backup. Two popular wallets already implement this. [2]
3) Contract security
This one is near and dear to my heart since I've worked as a contract auditor. It's still a problem but less so if best practices are followed, and projects which did so are holding vast sums without issues.
Of the two examples they mentioned, TheDAO happened when Ethereum was less than a year old and nobody had realized the reentrance issue; also it was nasty, convoluted code, and didn't have a thorough public audit. Parity actually had two problems: they changed their wallet, made a simple mistake, and it slipped through because they didn't bother getting a new audit. That enabled several large thefts. Then they made another change to fix that, still didn't get a new audit, made another simple mistake, and that resulted in frozen funds. Both mistakes would probably have been caught by any decent auditor.
As usual, keeping the code simple and straightforward helps a lot.
4) Probabilistic consensus
The new proof-of-stake chain is probabilistic initially but every six minutes it actually finalizes. At that point transactions cannot be reversed without destroying 2/3 of staked ETH. Currently the staked ETH totals $5 billion.
However, so far this is running on the side, with real ETH but not actually running smart contracts or transferring ETH around. It will be about a year before rest of Ethereum migrates to it.
5) Privacy
Zksnarks are able to help here and Ethereum is getting better at implementing them efficiently, but privacy is not in wide use yet, partly because of gas costs. EY has done a lot of work on implementing privacy in zkrollups for corporate transactions on the public chain.
6) Price volatility
For people unwilling to deal with volatility, there are stablecoins on Ethereum, some implemented as derivatives over ETH.
[1] https://vitalik.ca/general/2021/01/05/rollup.html
[2] https://vitalik.ca/general/2021/01/11/recovery.html