Im gonna make SimpleSEO has the option to do the dirty work of ensuring every link is https compatible.
So how it would work. There are many thirdparty site out there isn't https ready. That make the jobs seemingly impossible to get it done, but we have to try first before giving up, right ;) Example on how it works
There are links on my site look like: http://77.81.98.137/i/01/00235/87ko9y4bdbth.jpg
It's from vidzi.tv, and vidzi doesn't have a https website.
The plugin will scan the page content before render looking for <img src="http://some-site.com/some-img.jpg"> change the url into something like "https://yoursite.com/...ite.com/some-img.jpg". The remoteimg controller/action will fetch remote unsecured content and served it under your secured site url. Sound good right? Not that easy, that only works for images, I don't even have a solution for unsecured iframe content yet, but still we try, once day maybe we will get there. And by the way, I can't afford to to give away next version of SimpleSEO for free, but dont worry it's gonna be around 5-10 ;)