As Bitcoin advances towards adopting the Lightning Network, it should only be a matter of time before sidechains become implemented into it. These sidechains will work in a similar fashion to altcoins, allowing to extend Bitcoin's functionality including (but not limited to): smart contracts, micropayments, identities, and more.
As such, I believe that once sidechains are introduced into Bitcoin, there would be no use for altcoins as BTC would be capable of doing everything that most cryptocurrencies do today. In the end, altcoins might become obsolete, while Bitcoin will become an All-in-one cryptocurrency handling anything we throw at it.
What's your opinion on this? Will Bitcoin sidechains render altcoins obsolete? Or will altcoins co-exist with BTC sidechains?