Don't probation periods already exist?
It would effectively create a filter against ideal candidates.
It's a engineer's market right now. Find ways to make it easier for them.
Last year I piloted a project where I paid engineers ~$375 for 4 or 5 hours to work through code with me. By the end of it, if they were an engineer I would work with, I would recommend them to a select group of companies that I felt were the best places to work (great product, team, environment). The condition was that when I referred an engineer, they must be considered to have already passed the technical interview. At that point, they were simply there to see if they were a cultural fit and talk tech. Maybe some light technical questions, no white boarding or trivia.
This afforded the candidates the ability to fast track to the final round of an interview with 5-6 companies. And they got paid to do it.
It worked remarkably well, all parties loved, and it to this day I still get emails from companies and candidates asking if I'm still doing it. Alas, I a full-time founder and cannot do that anymore.
But should anyone want to take my idea, I can assure there is a demand for it, and it pays incredibly well.
It would be awesome as a candidate to take on five hour project and be able to apply anywhere and skip the technical interviews.
To do this, though, companies have to trust you and your referrals (send one bad engineer and it can be game over). You also have to ensure the companies don't waste the candidate's time or put them through another full round of interviews. This wasn't really a problem because there's such a demand for engineers and I managed the hiring process very closely.
If someone’s suggesting it to you: You deserve better.
If my assumption is correct, the candidate will fall in this situation if they didn't already clear up the expectations, roles and responsibility before/during the interview. A friend of mine recently found himself in a situation where they decided to quit after working for less than 2 weeks at an early stage startup. He ended up quitting by the end of the month.
I believe it's a shared responsibility to clear up such things before making an offer (from company's POV) or accepting an offer (from candidate's POV). This situation doesn't help either party.
The huge downside for the employer is that you're never going to hire away anyone from another company, so you're pretty much cutting out anyone who isn't very junior.
If they ask that means you are good enough for the job.