You should build this if you want to build it. It's something you can point to and say "Look, I built something awesome!".
But, chances are this will not be able to make money as it (1) requires user setup (2) will be fairly difficult to build - api integration is not that easy (3) most users simply don't care about what happens to their data until it is gone.
(3, my experience) goes directly against your Thesis #2. (1) goes against your Thesis #3 - users generally are not forward thinking enough to do something now that will only benefit them later. I'd say start on actually trying to test your Thesis #1-#3 before assuming them correct.
I think this identifies the issues I was feeling with the product, primarily the point that users are rarely forward-thinking. Instead, they use the single service that is hot right now, and don't look for alternatives until their current one starts to die. The thought that they'd have to set up multiple services (some of which might require a subscription and others that require new accounts) will probably scare many off.
That said, I think an MVP is the way to go on something like this (NOT something fake with a fake button; that's for scammy money-grubbers). There is probably a niche for something like this; the only question is if they will pay for it or not, and pay enough to keep the service alive. I know of photographers that would love a one-click upload to all the photo sites. Same with videos, tweets, and blog posts. Seeing if they will pay will simply require you to try it.
But, chances are this will not be able to make money as it (1) requires user setup (2) will be fairly difficult to build - api integration is not that easy (3) most users simply don't care about what happens to their data until it is gone.
(3, my experience) goes directly against your Thesis #2. (1) goes against your Thesis #3 - users generally are not forward thinking enough to do something now that will only benefit them later. I'd say start on actually trying to test your Thesis #1-#3 before assuming them correct.