That's not really true. Systems like Ethereum allow for arbitrary data storage and contract structures. The filter for consensus in a distributed environment will be usage. Lots of contracts will get written, a few will get used. Those few will be the ones people agree on.

Secondly, the consensus as to the schema isn't trustless even in blockchains. Deciding what to do and how to do it is and always will be trustful. What is trustless is the execution of that decision once its been made. That is the important contribution of blockchains.