Wouldn't it make more sense just to fix the URL bar to make data URIs look different? You could even go to the extreme of making it just show "data:…" and requiring you to put focus on it to find out the full URI.
No kidding... this is a problem they created by hiding/obfuscating the URL scheme. If the majority of URLs you visit start with http:// or https://, then data: stands out like the proverbial sore thumb.
That requires that you know what you're doing, though. Non-technical people are probably more inclined to think along the lines of "huh, odd, but everything looks fine, so it's probably my fault it looks like that"
Oh, I honestly would've missed this, because so few sites I browse are in cleartext anymore. They may as well just display a giant "INSECURE" banner, instead of http://, though.
Though it's still disabled by default (currently the insecure connection icon is only shown if a password field is present on a http page / the form action url is http).
