My final master project was about this topic and I agree that a service/app like this offers tremendous advantages. The difficulty with this is indeed what is mentioned below your suggestion, and I am not yet certain if safenet offers the right functionality to offer this. What I mean with functionality is that the company only gets access to the processed data. They have to develop their code, their code will be executed within a vault/sandbox open for validation and then the required data to offer a functionality offered by the company is send through.
As far as I understand most applications in development today on safenet are executed on the device itself and the (raw) data is then processed in the application, if a company would want to misuse your data they could develop a backdoor and copy and indeed sell your data.
Farmers are providing storage to the safe network but do they also deliver a certain amount of processing so these raw to processed data handlings can be executed in a/the safe environment?
This needs to be solved from a network perspective but then you also need a few important usability issues to be solved and included in the network capabilities. One of those would be the requirement of descriptive permissions. Currently in the test setup people have to agree with certain permissions to give an app access to their data. But for the average Joe this needs to be very clearly translated into: what data, why this data is needed and how valuable that data is. The value of that data can then be connected to the safecoin and the internal market. I would love to see this as a hard coded requirement, that the API (SDK) requires this the same way as the authentication keys are required to decrypt the data.
And of course we need to discuss about standardization for certain types of personal data. This means that if I store my home address on safenet using my insurance company, I don't get a duplicate data set when I am signing up for a newspaper that uses a slightly different format for my home address.