I agree that we're only partially solving the problem that comments were designed to solve by locking them up at 50 rep, or any level, because those who can't use them will continue to exhibit the behavior that they're designed to stop.
I don't want to put additional needless asks on people that spend a lot of time in review; indicating if a string that is often too short to be an answer is good or not good is just a waste of people's time. That would be turning /review into more of an unpaid Mechanical Turk than anything, I know this because I've spent years looking at comments left by new users that managed to earn 50 rep.
What I propose is simplifying it. Let anyone with a registered account leave a comment until n comments left by them have been flagged and deleted. If that happens, back to waiting for 50 rep they go. I know this is a little complicated, but enabling this softens one of the first sharp edges folks hit when deciding to engage.
Anything else I fear is going to require a hard look at our comment system and the tools available to moderate them (which, quite frankly, stink). I really think we should be looking at ways to reduce the amount of work comments create. While your idea would work, I feel very awkward about the ask involved with putting them through /review.
As for n - it would need to be quite low, as in 2 or maybe 3. Most people that would get access to this would end up being blocked until 50 rep anyway, and we need to be good with that. What this opens for is that occasional pearlpearl that wants to engage and knows how to do so effectively.
If this sort of thing is too complex to introduce, then we really should find something similar that isn't - I don't want to put additional load on our machine or human resources to deal with comments as a matter of principle - they're just not that important in the grand scheme of things.
Update
This remains a problem that we want to solve, but the solution I've come up with and those in comments just have too many potential pitfalls. The biggest problem is comment moderation tools aren't that great, and opening them up earlier, or lifting the rep barrier altogether just opens up the door to too much potential abuse.
What we should be looking at is why we can't take any of the rather good suggestions here and go with them, which comes back to the fact that we don't deal with comments as well as we should.
We're going to aim to fix that, as a whole, which should solve the issue of those needing them not being able to use them altogether.