Can Binance Smart Chain increase decentralization over time too?
I don't think that is ever going to happen. The most weird part is, no one cares that the whole chain is somewhat centralized.
These alt blockchains may seen cheap, fast and great right now but are they are truly decentralized?
Which altcoin blockchain exactly are you talking about? People say that Solana is not actually truly decentralized. At least not now, but will eventually become as more validators join the network. Cardano claims to have achieved 100% decentralization.
When Eth 2.0 comes out and people leave Solana for Eth 2.0 then how can Solana grow in decentralization then?
By the time Ethereum network fully upgrades to ETH 2.0, Solana will grow and take over enough supporter for it to survive the market. Why do we have to compare ethereum with solana or ada? They all can coexists without issue.
What test a blockchain must pass to claim the 100% decentralization status?
I don't think multiple smart contract blockchains can coexist unless they are compatible with each other that is a single smart contract that is compatible with all blockchains. For example can I borrow $1000 USDT against my Cardano collateral on a smart contract on the Eth blockchain yet pay cheap Solana fees?