What's practically possible is always a subset of what's legally possible. I think probationary periods/contract-to-hire situations are extremely unlikely to work for anything beyond absolute entry level, for a number of reasons.
For one thing, it's a huge amount of uncertainty to put on the potential hire, which means you'll be strongly biasing your hiring pool towards people who don't have better options. It feels like in an effort to reduce the interview time, you've effectively expanded it to multiple months.
Second, how do you calibrate the "default" option? Is the expectation that everyone on a probation period will be hired unless proven otherwise, or is it that most will be let go unless actively vouched for? Is that expectation clear across the team? If there's a mismatch across team members, you have big problems. People who want to keep a prospect will be annoyed if they're let go, and vice versa. People who need to work with a prospect will have to figure out whether it's safe to actually trust them with anything - on the one hand, you have to give them enough work to prove themselves; on the other hand, you can't give them anything too important or with too long a horizon, because they might be gone before they get to launch.
And finally - how long does that trial period need to go on to be useful? The goal in designing a hiring process is to get a reasonable level of precision/recall (different companies will balance differently between those) with a reasonable level of investment. If you've increased investment without increasing precision, then you've done something wrong. Given how long it takes to ramp up a new hire and have them actually be productive, I don't think you're going to learn much in a ~6 month probationary period that you couldn't already tell in a day of interviews.
The default option is simple: did the hire add meaningful value to the team? Very few people fail that simple test, in my experience; and folks who would have failed technical screenings would have excelled in subsequent performance-enhancing evaluations. Someone who can't balance a binary tree might be the single best technical coordinator you're going to hire, after all.
I've worked at many companies, and those that hire fast, and fire fast, tend to be those that _fire least_. They have _lower expectations_ for performance, and so are more likely to be receptive to _training new hires_, rather than expecting them to hit the ground running as equally effective as their new team mates.
For one thing, it's a huge amount of uncertainty to put on the potential hire, which means you'll be strongly biasing your hiring pool towards people who don't have better options. It feels like in an effort to reduce the interview time, you've effectively expanded it to multiple months.
Second, how do you calibrate the "default" option? Is the expectation that everyone on a probation period will be hired unless proven otherwise, or is it that most will be let go unless actively vouched for? Is that expectation clear across the team? If there's a mismatch across team members, you have big problems. People who want to keep a prospect will be annoyed if they're let go, and vice versa. People who need to work with a prospect will have to figure out whether it's safe to actually trust them with anything - on the one hand, you have to give them enough work to prove themselves; on the other hand, you can't give them anything too important or with too long a horizon, because they might be gone before they get to launch.
And finally - how long does that trial period need to go on to be useful? The goal in designing a hiring process is to get a reasonable level of precision/recall (different companies will balance differently between those) with a reasonable level of investment. If you've increased investment without increasing precision, then you've done something wrong. Given how long it takes to ramp up a new hire and have them actually be productive, I don't think you're going to learn much in a ~6 month probationary period that you couldn't already tell in a day of interviews.