I believe that when 2nd layers are build on Bitcoin, they can do same things as certain altcoins, but faster, cheaper and more secure. On top of that, BTC is accepted in more places, so it makes more sense to use this currency instead of an alt that almost nobody owns.
I think it is easier in the short term to create a blockchain for only one specialized user case, but in long term it is way more efficient when everything is done on one big blockchain. I think finally the lightning network will outperform Monero, Zcash, Dash enz. because it is anonymously, almost free and instant and if RSK is as good as they promised they will outperform ETH too.
The security of the Ethereum chain is way less and it is proven not tamper proof after the DAO hack and the network is kind of centralized. Also RSK will be cheaper. One new event like the DAO can push all the new smart contracts to BTC. The only advantage of ETH is that it is hyped by mainstream companies and banks and that BTC has to sell itself. But after al a good product will sell itself!
I hope to see more specialized frameworks with different economies, goals and functionalities working with their associated crypto-currencies, it makes more sense to me. But you gave me a good topic to study in deep since i'm still a newbie in the "crypto-world" and RSK is something I've heard, but still pretty ignorant about.
One thing is certain, the crypto economy may reshape our world as much as smartphones or internet did. It will be fun to watch :-)
p.s. Sorry for my not-so-perfect english.
We will see how the future plays out, but I see the Bitcoin blockchain as an extremely secure, super valuable core were 2nd layers can be build on in form of side chains, off chain solutions and applications with all specialized functions and abilities.
They will be suited for different uses and economies. Thats why I think some people that are heavily invested in altcoins are trying to block Segwit in Bitcoin. Segwit will be the fundament of 2nd layers and is very well tested. It doesn't make any sense to block it if you want Bitcoin to move ahead.