Actually I am building one such service now. The key factor has been realizing how bad the cross-provider toolkits are at really exposing their feature sets, in the places that they don't like to talk about: some of those listed above. Essentially, right now, you have to build it yourself. There are toolkits, but none of them are effective. I emailed an academic working in this area circa new year to compare notes, but am yet to receive a response.

ie: The assumption is that any given provider may fail, any given provider site may fail, any given provider host may fail. You have to have a programmatic, automated response for that.