It wouldn't be a perfect solution, but I wonder why browsers don't indicate the registration date for a domain in the URL bar somehow? I bet junon would have seen that and gotten suspicious.

I like this idea and could see it being visually represented as a faint red/green bar behind the URL text in the address bar, with a greater amount of the bar being red when the domain is less trusted.

As for developers trusting a plugin that reaches out to an external location to determine the reputation of every website they visit seems like a harder sell though.

that's a good one not perfect for sure, hackers would just start buying domains earlier but still...

There are curated lists over newly registered domain names that some security software uses so it should be easy to add without any privacy issues.