Robuta

https://bitcoinmagazine.com/technical/sourcing-bitcoin-lightning-liquidity
To actually solve the problem of receiving funds without having secured liquidity from someone else's node requires protocol-level changes.
lightning networkproblembitcoinliquidityideas
https://bitcoin.design/guide/how-it-works/liquidity/
A primer on lightning network liquidity
lightning liquiditybitcoin design