Bitcoin's fungibility is clearly a problem, but Lightning mitigates it even more than privacy coins. I think standardizing payjoin would be a good solution to increase on-chain privacy, and Bull Wallet has already shown that it can be done asynchronously.

Bitcoin is fungible money. nostr:nevent1qqs8arhmgdy09785qcrhs0j9h394psa9ajp9pgs3nlqugv0u7ycnkmgpzpmhxue69uhkummnw3ezumt0d5hsz9thwden5te0wfjkccte9ejxzmt4wvhxjme0qy2hwumn8ghj7un9d3shjtn90p5hgtnsw43z7grg78c