Of course they do. it sounds like you just phishing for confirmation that holding only bitcoin is a good choice. Not that that is a bad choice.

I also would guess by "future" you mean financial success of a booming coin price which is not necessarily the same thing as bringing a good use case with better/different tech than bitcoin.

Bitcoin will be used for certain things but not everything envisioned by Satoshi. Store of value and sending large amounts with low fees internationally, yes. For privacy and fast zero fee transactions of small purchases, no.

Maybe so, maybe ether.