I think one missing piece is inflation. I focus my effort in this direction. Check out my project:
Here's the thing, in 2014 I was playing around a bit with Bitcoin, and at that point adoption seemed better than it is today. I could buy a cup of coffee with it, and many reputable online storefronts were already experimenting with accepting it as payment option. Later, long transaction times and high fees made it almost impossible to actually use BTC as a currency.
My perception is that Bitcoin used to be a serious currency project, but got co-opted by speculators, miners and scammers wishing to use it to accumulate fiat currencies quickly.
Easy fiat onboard do not exist, and none seem to be coming. All of them you need to do KYC and interact with the main chain, its super unuser-friendly, or require debit cards.
Taxable events get triggered when transacting with bitcoin. Really hard to manage and a really undesirable side-effect for a consumer.
The need for watch towers and inbound-outbound capacity make the technology hard to understand not usable by mainstream.
The lightning network seems to be heading toward centralization, then what it the point? Is the delta of Credit card transaction fees with lnd fees that big that it warrants it? especially if credit card fees drop with time.
Lightning tries to live up with Bitcoin's ethos. It's designed with decentralized nodes. We end up with 2 decentralized networks trying to talk to each other. The result is a very complicated 2nd layer. I think centralization can simplify a lot of things. As a user, I don't have a problem with it. Exchanges are already centralized. We just need more options to choose.
I'm excited about 2nd layers. I think they would enable Bitcoin to interact with other technologies. I created Bitflate based on Bitcoin. We can mix Bitflate and Bitcoin to create hybrid coins. Some level of centralization is fine. It's a tradeoff for lower cost and better UX.
There is a massive difference between temporary centralization for convenience vs. fundamental centralization. See email. Gmail basically has the entire market, but that is a world of difference from email being a proprietary private Google protocol. People can switch at any time. If a provider misbehaves they can be abandoned. The users have the power. The same holds for complaints against coinbase, the internet in general, etc.