If you don't want to give full access to all your data, check out https://starthq.com. We do federated search from the client via an extension. There's also an API which lets you add support for any service you want: https://starthq.com/developers
We haven't been actively working on it for a while, so have been considering open sourcing it. If anyone is interested in helping out with that or has ideas as to how to monetize this, drop me a line (hello@starthq.com).
Have you also considered the Pillar Project's approach? They too struggled for funding, but I rather like the connection among blockchain technology, ICO funding, and personal data tools. I think the inversion of control that these efforts are seeking is what society needs in order to have a more healthy relationship with companies (and governments).
We haven't been actively working on it for a while, so have been considering open sourcing it. If anyone is interested in helping out with that or has ideas as to how to monetize this, drop me a line (hello@starthq.com).