Interesting ideas and I agree strongly with most of it, but I do take issues with a couple of points.
The consultancy or probationary period is the one I find most objectionable. This works fine if an individual is out of work, but the majority of people you’d want to hire are already employed and looking for a change. Asking them to quit a current role so that you can audition them for a month is something very few people would accept. There’s always the chance it won’t work out and now you’ve gone from employed and looking for a perfect fit to unemployed and needing to find a new role ASAP. An audition project that is smaller and can be worked on over a weekend or in free time can work great, I think.
In addition, although commitments to open source work is great I know many programmers who haven’t worked on anything that isn’t proprietary and confidential since college. It isn’t that they don’t love their work (although that is possible of course), but would rather spend free time with family and devote extra time, when it exists, towards advancing prospects with their employer by working on “nice-to-haves” there. In many cases this is an employee you’d love to have, but may completely lack a public portfolio.