Well that's the question that if someone truly knew they'd be a very wealthy individual. No one knows but u can do research/make educated guesses.. When it comes to protocols that are primarily used for value transfer, *my educated guess* is theres only room for bitcoin and maybe 1 or 2 others. & the others would more than likely have significantly smaller market caps. I think LTC is a strong candidate simply bc it was one of the first alts to take off and got lucky by the fact that many of the Chinese who trade it don't really think of it as an altcoin. But I don't think it will increase in value relative to btc much (prob just fluctuate within a certain trading range) notwithstanding the extremely rare event that something happens to btc that doesn't affect LTC at all. XMR also has an interesting value proposition imo. Fungibility is an important characteristic of good/sound money. While bitcoin can improve on it's fungibility with things like zcash, it can never be as fungible as XMR is at it's core. This allows monero to make the claim it's more like digital cash, where btc is a decentralized distributed ledger.

When you get into the ethereum type projects/coins i am more uncertain where this goes. Will btc be able to eat ETH's lunch with rootstock etc... idk. I think there's a non trivial chance ETH or an ETH like technology shares a major portion of the crypto pie. Just too early to tell if/what and im observing that space on the sidelines for now.

At this stage of the game, I think it's smart to keep at least 70~80% of your crpyto wealth in BTC