Proposal: multiple formats per page using layouts

As far as I can tell, it's not possible to have two output formats for a single page/post at the moment.

We have a case where we'd like to generate an iCal file for each post, as well as the HTML version. It seems to me that a nice way to do this would be to allow multiple extensions for each layout, and generate a file for each extension in the specified layout.

For instance, if we had a post 2014-10-30-hello-world.md, and two layouts, _layouts/post.html and _layouts/post.ical, you would end up with output in both /2014/10/30/hello-world.html and /2014/10/30/hello-world.ical.

I'll have a go at this when I find time, but I was wondering if anyone could highlight any fundamental reasons why this wouldn't work, or problems that might be encountered when writing it?