Its volatility and UX, as well as how negatively it is perceived currently (by some people) look like bigger blockers to me.
Lightning will definitely not solve it.
edit: tps -> transactions/day
Lightning is a way of using bitcoin. A way of cooperatively creating bitcoin transactions with multiple parties, in such a way that you can minimize the number of on-chain transactions required. It is bitcoin. It has the same security model as bitcoin. It uses the same technology. It is not in any way centralized (it's a p2p network of payment channel connections, with each operator running their own server).
Even worse, if you saw my transaction, then sent me 1BTC worth of goods, then your node becomes offline and I forcefully close the channel with the original balance, I still have my 1BTC and there is no proof anywhere except your node that the transaction ever happened. So no security, unless both nodes are online.
Finally, unless you open direct channels with everyone you want to transact with, you will rely on a 3rd party node that does have such a channel. In practice, this likely means you will use one of a few major nodes that you trust to stay online and not refuse transactions, so the payments are in effect highly centralized.
A system that validates new entries into a database can either be "very cheap and very fast" or "very fault tolerant and very decentralized". The speed of light in networking and the speed of modern CPUs make this unavoidable.
Which that is not Bitcoin and neither is it on-chain.
The parent comment is correct on Bitcoin's failure as a peer-to-peer electronic cash system and all it is instead, is a store of value. This is how you know it has failed in its intended purpose.