When was the last time you saw a web app that was a single html file and nothing else?

Around the same time I saw a web app that was a single SWF file that you could email. I do see tech demos in that form factor though. Or at least they could easily be.

With resources embedded in the highly "compressed" base64 encoding. Quite a few email services will probably block those html files just because they end up stupidly large unless your content is text only and doesn't include half a dozen java script frameworks to manage basic animations.

Those same email services blocked SWF files too because they were dangerous. This is no different.

As for size, browsers really should allow gzip encoding for html files from your desktop. Would pack all the inlined crap down to a reasonable size and then you could transfer things around better.

Not if it has local dependencies, like js or css, then you would need to bundle those as well, in an archive perhaps.

You can include js and css in the same html file, between <script> and <style> tags.

Duh, that's if I build the page myself and I know how to code html. Even then it's not trivial in the sense that it will "just work".

What could possibly cause it not to work?

A grandma saving a html page and sending it via email without having to edit the html.

That grandma probably wouldn't have had much luck with the swf either.

For the purposes of email inclusion, there's really no reason not to inline all that stuff.