Yes things have been done, but nothing that's effective.
Any layer-2 solution is just a dead end as you still have to pay the high fees to enter and exit. And it's funny, and sad, that you bring up Liquid as a potential solution because it's a centralized solution and we might as well be content with PayPal if we're going that route.
I don't consider it a solution, I consider it a reality.
If you want to transact in unlimited amounts very quickly, there are extremely viable options. If you then want to pay a little bit more to custody your asset in the most secure way onchain, you can do that. Let's step back and look at the criticism: we are still talking about nearly instant on-chain settlement, and by instant I mean within an hour, at any time of day any day of the week.
We are talking about fees lower than what trading commissions were for decades, but being mad that it isn't simultaneously better than merchant processing fees or for poor people all the time.
There is just a parallel world here with plenty of options, completely accessible now with atomic swaps or bonded minting/burning in a way that wasn't available even just two years ago. The exchanges are mostly irrelevant except the largest fiat onramps, which have recently expanded too.
That's where we are. If the market really wants to get frothy this time, I think the capacity is quite ready. And for things that aren't ready due to programming or people just not using them, they incentivize is there to be a catalyst.
what high fees to enter and exit. Lightning fees are very low (typically( about 0.00001 pence. Liquid is not needed for lightning. As an end user you can use a lightning wallet and enjoy fast lowest fee transactions.
You need to pay for an expensive on-chain Bitcoin transaction before you can use Lightning. You must also have enough money so you can pay for another on-chain transaction if the channel closes and you must issue a dispute to not lose your funds.
Did I mention that if you open a channel to the wrong hub, you must open yet another channel, with all associated costs?
It's ridiculous to even entertain Lightning as a viable option when there are other low-fee and fully functioning cryptocurrencies that aren't gimped by a tiny blocksize.
I am sorry. As a lighting wallet user, none of that is true anymore. The underlying channel management is abstracted away from the user. The experience is pleasant. I won't jump to another cryptocurrency as BTC with lightning ticks all the marks for me.
The only thing missing in the BTC ecosystem is smart contracts, but I am happy for that to be a separate ecosystem (ETH or otherwise).
Any layer-2 solution is just a dead end as you still have to pay the high fees to enter and exit. And it's funny, and sad, that you bring up Liquid as a potential solution because it's a centralized solution and we might as well be content with PayPal if we're going that route.