The current standard says that a claim which cannot be provided by the OP should be omitted in the response. Likewise if the RP requires a specific evidence/method and if the OP cannot fulfil this requirement, the response will not contain this information.
If the RP now receives such a partial dataset which it is not able to consume as the requirements were not fulfilled entirely, the RP cannot do anything with the data and needs to throw them away. Still, the RP might get charged for the data transfer by the OP as some data was provided. This makes the financial aspect tedious/complicated.
We should introduce the possibility for an RP to specifically state that if a specific requirement cannot be fulfilled, the whole transaction shall be aborted instead of partially completed.