I believe that our community's increased awareness of side-chains and spin-offs (
https://bitcointalksearch.org/topic/spin-offs-bootstrap-an-altcoin-with-a-btc-blockchain-based-initial-distribution-563972) will be sufficient to reduce the market cap currently held by alts. Why would you want to invest bitcoins in an alt-coin, if a side-chain or spin-off can assimilate any technology that proves useful and automatically distribute it to a wider user base (and for no cost in the case of spin-offs)?
That being said, I think coins that don't offer any technical improvements over bitcoin, but instead strongly appeal to subsets of the community, may be unaffected by side-chains and spin-offs. Take DOGE for instance. DOGE is not technically innovative, but instead derives its market cap from its usefulness to its like-minded community. It's community is the intersection of those who:
- believe that a permanently-inflating money supply is superior;
- like the idea that their money is meme'd after the shiba inu bread of dog.
If this community forms an economy of like-minded people I can see it surviving, and growing but only to a limited extent since the pool of potential new users must also prefer permanent currency debasement and Shiba Inus. On the other hand, members of the DOGE community may slowly come to view Shiba Inu's as silly and currency-debasement as wasteful.
What is interesting is that right now the market cap of DOGE is about 64,000 BTC . However, as cryptocurrency grows, if bitcoin grows faster than dogecoin (due to DOGEs specific appeal to a smaller subset of all humans), then the DOGE market cap will fall when measured in terms of bitcoin.
If the reality is that most of the DOGE community actually likes capital gains more than Shiba Inus memes and currency debasement, then they would be incentivized to sell DOGE in favour of BTC. Now what is really interesting, is that although the DOGE market cap is 64,000 BTC, there is no way for everyone to get out of doge with anything close to this. If there is a stampede out of doge, the community will lose wealth in aggregate (actually that wealth was never there if this is the case).
This means that members of the DOGE community (or other niche-based coin communities) really have to ask themselves: are we in this because of our like for the Shiba Inu meme and our belief in currency debasement? Do we really believe that we can build a real and lasting economy around the shibe?