Bitcoin code suffers from mining attack vulnerability.
1] Mining attack. If Bitcoin suddenly loses a lot of mining power, block creation slows well beyond the 10 minute average. This is especially bad if it happens at the beginning of a 2 week cycle where the difficulty was just changed.
Possible resolution: Change block difficulty to exponential moving average difficulty of the last n blocks, where n is probably a fairly small number. 2 weeks is too long, making fees enormous and the network vulnerable. This could be done as a soft fork by changing the algorithm at a future block number, giving everyone time to update their software and/or hardware.
2] Mining centralization. Related to point 1, consider soft fork change for proof of work change. ASIC mining hardware causes centralized mining. While not necessarily a bad thing, it still allows hash rate to quickly move away from bitcoin in large percentages.
Possible resolution: Support SHA256 and the new proof of work for a range of blocks would be necessary, and at the end of the range, it would fully switch to the new proof of work only. Not sure what a good range would be, but enough to give everyone ample time to update their clients. Related to this, build a miner into the bitcoin core GUI should the proof of work change.
3] Allow block size to grow over time, maybe annually or every n blocks it is allowed to grow by some percentage or mathematical forumla. After 9 years, hard drive space is more plentiful and Bitcoin could take advantage of this at a smooth steady pace, taking advantage of ever growing space on hard drives. Blocks could also be compressed using modern compression algorithms such as ZStandard.
Hope the suggestions are helpful, I am fairly new to cryptocurrency and may be missing some things in these observations.
