If this works, then people are very gullible. It starts with fakery, as the email can't be plain that it is the start of a standard recruitment process, but says "...to tell you more about what we're up to" in a mock-casual way. But of course they'd never tell you something that isn't ready for public announcement because at that stage no you do not have a special relationship with the company and might even have a stronger relationship with a competitor.

Every company making cold calls to candidates pulls these sorts of tricks. If you want to make yourself stand out enormously, and seem incredibly different from every other company approaching candidates over email, LinkedIn, StackOverflow, etc, then something you could do is look into the candidate's public material enough that you can start by telling them the offer you want to make ($xxx,xxx), assuming there is a cultural fit.

For a lot of engineers there is a bucket load of the stuff out there. Tech talks on YouTube, even from the smallest local meetups these days. More code on github than you could get them to do in a thousand technical interviews. If they did a PhD, or even an honours dissertations, it is probably on the web and will tell you in great detail what they're interested in and how they went about solving a tough problem.

If your email started with the fact that you're interested in hiring them, here's the things you've already looked through, and so this is the offer you'd like to make if there's a cultural fit, that will make a candidate feel like you really have done your homework.