I will say Litecoin and... I hate to say this, but I think XRP has a potential.
Litecoin always being treated like second best coin after Bitcoin, even though it's not that popular, but it's safe.
While XRP is really centralized and banks friendly, since ETF is a government's product, so they can easily approve XRP since the coins are in their control.
Many people voted SOL, but I doubt with it, SOL is only popular recently, it's kind of hype.
Although BNB is fourth biggest market cap coin, their market cap can be so high due to Binance, if the exchange fall, BNB will become worthless, so it's risky for government to launch the ETF version.
Litecoin, no. XRP, maybe. Litecoin have had no major developments in years, XRP still has some regulatory hurdles. Despite the hype solana currently has, it's going to take a long time before it can get it's own ETFs. Their ecosystem still has a lot to prove tbh that it's not just a chain for pump and dump memecoins. My opinion is that it's going to take awhile before we start seeing new ETF buzz for another altcoin after Ethereum. It won't be anytime soon.