- UI/UX/user-friendliness: Bitcoin might be easy enough to use for most of us here, but it's definitely not for non-tech savvy people(e.g. our grandparents). Especially with the handling of private keys; I don't think we can expect true global adoption if people needs to backup their recovery seed on pieces of paper.
maybe it is just me but i think this is no longer the case with bitcoin. it used to be a lot more complicated to use it before but nowadays there are just too many wallet alternatives and many of them are pretty easy to use specially the web accounts such as coinbase are very newbie friendly and they can even buy bitcoin through them.
It has definitely improved A LOT compared to how it used to in the past. But I personally think(and I'm pretty sure other people agree too), that the current state of bitcoin wallet's isn't enough for true global adoption. People forget their passwords all the time, what more their private keys? Using exchanges like Coinbase as a wallet is definitely not a good solution.
I believe using a web wallet is a bad practice for security. but it is really practical for some regular user to use cryptocurrency. Nevertheless, those UX design is yet still cannot reach for mass adoption. The whole UX design needs to be improved to make bitcoin ecosystem easier to use for the non-techy user.