What's a good way, or a good example to encourage people to apply if they think they'd be an asset to our team even if we have no real open positions that fit them?
You are basically describing a head hunting operation. Connect with a head hunter and let them do the vetting, instead of wasting so many people's time for a job that is going to be 20 levels away.
You have the gig, or you don't. Or you're a headhunter for a single job that maybe might be available some time way out in the future. That would be a waste of everyone's time.
We've yet to catch a superstar with this strategy.. I wouldn't even call it a strategy. At one time we did have these positions open and ready to fill, we just never took them down after filling, just to see what trickles in.
Doing this for people who applied for, but didn't get, the real job is fine. Continuing to do it when the job is no longer available is a kind of surveillance.
If that will get you a good number of results is the other question.
If you’re always hunting for unicorns, say so, but IMO collecting resumes “just in case” is a waste of everyone’s time, and collecting them under false pretenses is way worse.
Gotta wonder though, what thing X would you do with such a 'hero' if they appeared, and why aren't you doing X already, upskilling the people you have in the process?
This feels like a magical-thinking policy not a strategic one? If there's no clear goal for the continuous search, don't do it; it wastes everyone's time. If there is, advertise that job instead.
Good luck!
But I myself wouldn't submit anything to a company this way unless someone at the company suggested it.
And I suspect that people who send their resumes this way are either junior developers looking for job, or developers who are desperate for a new job. So I'm not sure how many diamonds you might get.
I'm old, been in this business a long time but never really on the hiring side. And the few job switches I've done have all been because a contact convinced me to come on over sorta thing.