Trying to understand what we should expect after External Owned Accounts will be treated as Contracts after second Serenity update will be live.
How does it influence ERC223 Tokens, will they break or continue to work ?
In current understanding, Serenity will be a separate blockchain, so no contracts will automatically migrate from current Ethereum to Serenity. New token contracts deployed on Serenity will probably require new standard interfaces, different from EIP20/EIP223 etc., though it is too early to tell what exactly the differences will be.
Serenity will have a link with existing Ethereum blockchain allowing assets transfer from old chain into the new one. Thus, new token contract on Serenity will most probably need some mechanisms to facilitate such transfers.
The changes are so severe that it will a require an entirely new blockchain, with a backlink to the existing proof-of-work chain. The long-term goal is that once the system is stable enough, all the applications on the existing blockchain will be folded onto a shard on the new chain. This means the new chain will be fully compatible with the old one while enabling it to scale.
So even if and when old blockchain will become part of the new one, the old blockchain will still follow old rules.