Instead of ranting, can you say something constructive?
I can think of 3 paths to improve situation (assuming that "everyone deploys cryptographic email infrastructure instantly" is not gonna happen).
1. The email client doesn't indicate DKIM at all. This is strictly worse than today, because then the attack could have claimed to be from npmjs.com.
2. You only get a checkmark if you have DKIM et al plus you're a "verified domain". This means only big corporations get the checkmark -- I hate this option. It's EV SSL but even worse. And again, unless npmjs.com was a "big corporation" the attacker could have just faked the sender and the user would not notice anything different, since in that world the authentic npmjs.com emails wouldn't have a checkmark either.
3. The checkmark icon is changed into something else, nothing else happens. But what? "DKIM" isn't the full picture (and would be horribly confusing too). Putting a sunflower there seems a little weird. Do you really apply this much significance to the specific icon?
The path that HTTPS took just hasn't been repeatable in the email space; the upgrade cycles are much slower, the basic architecture is client->server->server not client->server, and so on.