I think finally Bitcoin will be the only standing because it is the ONLY cryptocurrency that is very wel suited as store of value and this can never be replicated by an altcoin.
In my view eventually all altcoins will replaced by 2nd layers of bitcoin because they have the best security for free. HODLers pay the miners already, an alt that has its own blockchain need to pay the miners for a smaller level of security.
Over the long term an own PoW blockchain is simply not efficient (less security for more costs) and PoS will lead to centralization. Beside that with 2nd layers you can use BTC and that is most used and accepted (network effect). 2018 will be the year that the first 2nd layers will be rolled out! (Lightning Network and Rootstock)
Thats why my strategy for a few years already is HODLing 80% in BTC and use the other 20% for picking interesting alts. When the alt made a return of 20 to 50x I sell a part back for BTC, so slowly grow my BTC holdings.
After selling a part simply let it grow to a big stack again and repeat the same. This way you have a relatively steady portfolio and you will always be holding a small amount of interesting alts.
Bitcoin is the grand-daddy G, so there is no way it will lose its spot in the top 3. However, I just don't really see the benefit of holding bitcoins this late in the game. Sure, I got a few, but I wouldn't put all of my investment in it. Call me a traitor, but my hope is in Ethereum and Ripple. We are heading toward a whole new gaming revolution using the Ethereum block-chain and I can see its potential. I can smell it. I can taste it. Ripple, on the other hand, already has banks backing them up and I will milk everything I can from them. My strategy is a bit similar to yours. 80% of my investment is spread out evenly among the top 3 cryptocurrency and the other 20% is in the altcoins that I am interested in (gaming and virtual reality).
I think many people underestimate the potential that BTC still has. Hedgefunds are just started and will bring way more money in. Some later all the extremely rich will go HODL their wealth in this store of value and also central banks and Governments could finally go in. What do you think about international trade / import and export?
There is still HUGE potential for BTC (million per coin = 100 x is possible, will be 3 times the market cap of gold and since the usability is way higher......) and I expect the day will come that every powerful entity on the planet want to own an as big as possible part of the BTC blockchain while the supply is limited......... Alts will be forgotten if this happens.
I think the steem dollar will completely replace and eliminate bitcoin like it is currently on track to do.
https://steemit.com/steem/@mysearchisover/steem-is-beating-bitcoin