Q:

Will the introduction of sharding have an effect on the functionality of currently deployed smart contracts or the EVM?

Is there any risk the the hard fork required for sharding or Plasma to take effect on the Ethereum network will cause compatibility issues for contracts already deployed? 
Will the protocol in place whenever sharding is enacted be backwards compatible with current contracts (such as Tokens, etc).
Thanks for any help. I'm struggling to understand how it will effect this aspect of Ethereum.

A:

Phase 1 sharding won't have any execution or EVM, so it won't integrate with the main net. Phase 2 will have an EVM, and will introduce backwards incompatible changes at a smart contract level, like storage rent, however the intention is to try to make these changes as DX and UX friendly as possible. (See https://github.com/ethereum/wiki/wiki/Sharding-FAQ#you-mentioned-transparent-sharding-im-12-years-old-and-what-is-this; also see the links at the storage rent point here: https://github.com/ethereum/wiki/wiki/Sharding-roadmap#phase-2-evm-state-transition-function.)
Basic sharding design: https://github.com/ethereum/wiki/wiki/Sharding-FAQ#what-might-a-basic-design-of-a-sharded-blockchain-look-like.
As an L2 solution, Plasma will have to be compatible with whatever the current blockchain spec is.

