Here's how things are looking in 2021:
(1) Scalability Issues
Solved - there's a plethora of high-throughput chains in development, either based on sharding or pipelining/MVCC/optimistic concurrency. Some projects like Solana use GPUs and JIT compilation to achieve well beyond 50k tps in a distributed network.
(2) Lack Of Intuitive Private Key Management
Little progress. Ledger and other hardware wallets make things easier, but it's still far from intuitive. Non-technical holders typically use centralized custody providers.
(3) Contract Security
Some progress. Smart contract exploits still happen almost every week, but there's a robust set of best practices, safe-by-default standard libraries, and specialized auditing companies which make it much easier to write bug-free contracts, if you're willing to invest the time and effort.
(4) Consensus Algorithms Are Wack
Solved very thoroughly. There has been significant progress in byzantine fault-tolerant consensus, like Tendermint consensus[1] used in the Cosmos ecosystem, providing strong consistency and instant finality.
(5) Privacy
Many developments around zero-knowledge proofs and similar methods, but I don't know how viable those are.
(6) Price Volatility
There's a number of trustworthy stablecoins like USDC pegged to fiat currencies. Other than that, tokens are still highly volatile and only useful as a high-risk investment.
[1]: https://atrium.lib.uoguelph.ca/xmlui/handle/10214/9769
(1) Scalability Issues
Solved - there's a plethora of high-throughput chains in development, either based on sharding or pipelining/MVCC/optimistic concurrency. Some projects like Solana use GPUs and JIT compilation to achieve well beyond 50k tps in a distributed network.
(2) Lack Of Intuitive Private Key Management
Little progress. Ledger and other hardware wallets make things easier, but it's still far from intuitive. Non-technical holders typically use centralized custody providers.
(3) Contract Security
Some progress. Smart contract exploits still happen almost every week, but there's a robust set of best practices, safe-by-default standard libraries, and specialized auditing companies which make it much easier to write bug-free contracts, if you're willing to invest the time and effort.
(4) Consensus Algorithms Are Wack
Solved very thoroughly. There has been significant progress in byzantine fault-tolerant consensus, like Tendermint consensus[1] used in the Cosmos ecosystem, providing strong consistency and instant finality.
(5) Privacy
Many developments around zero-knowledge proofs and similar methods, but I don't know how viable those are.
(6) Price Volatility
There's a number of trustworthy stablecoins like USDC pegged to fiat currencies. Other than that, tokens are still highly volatile and only useful as a high-risk investment.
[1]: https://atrium.lib.uoguelph.ca/xmlui/handle/10214/9769