I don't think ETF of other altcoins will have any impact in the price. It is all priced in now.
We can see the case of Ethereum ETF. The ETF was approved shortly after BTC ETF, and the price simple didn't move.
This will probably happen again with SOL.
I am a bit skeptical about SOL, because I don't think memecoins are worth anything. And as a memecoin platform, I don't see much future in sol.
I don't like Solana either, nor am I a fan of meme coins. Still, we can't ignore that a large enough number of people love them and they have their speculative value where the price can explode and tank rather quickly. I think solana might perform differently than ethereum because of its "made in USA" status. Who knows, maybe the orange man will include it in his crypto reserve, since we are no longer talking about only a strategic reserve of bitcoin and it looks like he has other ideas.