When one makes a GDPR Subject Access Request (SAR), one can specify a particular form of response, for example by email. Also the data can be requested in a structured, commonly used and machine-readable format. If one requested the response be provided via a web form would the data controller be required to use that form, or could them deny to provide the data if this was the only method available?
The case I am considering stems from this question, where from a single web site visit it appears there are 389 entities handling security. If I was to make a SAR to each, processing the responses would take a long time, particularly if some provided responses that were incomplete or in a non-machine readable format, and I had to chase them. It would be much easier for me to set up a website that allows data controllers to upload files and associate them with portions of the request, validates that they can be read by a machine, and allows submission only when complete. I would send the requests from a no-reply email address.
Would requesting the response to a SAR in this form be valid, in that failure to complete a submission on the web form would allow one to seek to enforce one's rights through the courts? Assume the information requested is unambiguous, eg. "what data do you have, where did you get it, who have you given it to", and the SAR request includes all possible identifiers (in this case, IP address requests were made from, content of all cookies, uri's of all tracking images and browser User-Agent).