My opinion is we dont need too many chains, as more asset types can be available on the same chain (its easier to write a smart-contract between assets natively on or pegged to the same chain).
Something else to say about pegging is you should be able to peg a contract from one chain to another, not just bitcoin or issue assets as a combining mechanism. eg so if someone compiles up a bitcoin denominated ethereum sidechain you could peg the contract out of it into a snark contract sidechain it with more privacy and a different contracting language between something issued there and pegged bitcoin or something else pegged there from somewhere else.
So sidechains give you composability of contracts in different languages and chains. Its like the decentralised and secure ABI of blockchain coding.
Adam