Added 2: This is in repsonse to the edit of OP.
First, the decision was never really "in the hands of the author." It was "in the hands" of various entities, including the author (with some exceptions, but let us ignore this). Other entities, in whose hands this decision was, where a) the moderatots b) the system (by which I mean auto-CWing one edits or number of answers).
And this was not at all only theoretical. There were cases of questions that were made CW by moderators against the explicitly expressed wish of the author (to be clear I fully support these decisions).
For b) this also happened, at least upon edits (I think for the answer threshold it was mostly done before manually), mostly by accident, in an irreversible ways. (This persists but now can be reversed, which one also can see as improvement, although to be fair one could keep this improvement and still go back to the old way regarding other aspects.)
Now, depending on how you read the above you might think this is nit-picking, however, what this also shows is that in my opinion and this is the point I want to make here:
The decisions if a specific question is to be CW or not was all the time much more a matter of following guidelines [edit: replaced a word] regarding the type of questions that should be CW than an actual decision of the author. Some authors that knew about the guidelines merely did it right away.
Second, regarding the "nothing to fear." Well, I am not so easy to scare, at least not by questions on MO, so no we have nothing to fear. But then since also the comparison to other sites is made where this might be an issue but here on MO it is not. I really recommend the blog-post I link below. The type of problems (if one sees them as problems, as some though not all do) on other sites described there are precisely analogous to what we have on MO, too. (As a general aside, while I agree MO is in some ways special, I think we should also avoid to overdo pointing this out, because then in various ways it seems to me the problems are in fact quite similar, and the situations are not that different.)
Third, for the specific qustions mentioned as example. It is even not so clear in my opinion that this must be CW for intrinsic reasons, and a slight modification (sharpening/improving the questions slightly) could make it in my opinion easily a non-CW question. (Again, I refer to the blog-post.)
This example to me seems precisely like one where CW is "abused" (this is not directed against the author, it is a common use here after all). My reading of CW-ing here is, [added: this is as indicated by the 'my reading' my personal interpretation, and could be wrong, but there were examples where things like what I say below were made explicty by an author or by others in discussion] that the author was well aware there could be opposition to such a question (whether this is good or not is not the question), and it has three votes to close at the time of writing, yet via entering the CW grey-area thought to avoid some of it, and sufficiently much of it that the question "survives." This is precisely how CW should not be used (that it was done a lot in the past does no change this).
Added: since apparently there is a considerable interest in my arguments (with 5 upvotes on the comment demanding them while half-way they are in comments already) here is one reason why I prefer the new systme over the old one and also the proposed one (somewhat redundant with comments):
A main point why I prefer the new system is that it should minimize certain small debates in comments that I do not find very productive.
The question of whether a question is CW or not is ultimately pretty much to the irrelevant end, in my opinion. In particular, this is not a very urgent matter. I agree some questions rather should be CW, but if they are not for a while early on it also does not change much.
But, for some reason some people seem to have relatively strong feelings about this (to avoid confusion, I do not mean Todd Trimble). Also, some, and sometimes the same approach this CW matter in ways I find strange. Berating users where it is really reasonable they did not know about it, or even worse could not even make it CW by themselves, some even voting to close over such things, which is one of the more inapproriate reasons for a vote to close in my opinion. Leaving comments like: "this is a community wiki question, voting to close until it is so labeled" (the until is an additional strange detail, but anyway).
Or, and this annoys me really a lot out of principle: ask OP to make it CW and at the same time answer the question in non-CW.
It is a mystery to me how one can justify to do this. It is particularly annoying (but some seem unaware of this aspect) since then even if OP reacts in a timely manner moderator intervention is needed as the answers stay nonCW and CW is mainly so that the answers are in CW so a quite absurd situation arises. But even if I would not know this I cannot understand how one can ask for it to be CW and not oneself set the accompanying example.
So, in my opinion, each such event reflects negatively on the site. With the new system this is a lot more unlikely to happen in this form. This is an improvement.
The main reason for it is AFAIK is to discourage the type of questions that got asked in CW. See this blog post http://blog.stackoverflow.com/2011/08/the-future-of-community-wiki/
There were debates surrounding this, so it is somewhat unlikely this will be changed (in the sense that others raised the same point with similar arguments we might make).
To your specific suggestion, I would be against introducing a rep limit, since this will only create confusion. (More generally, I consider the current situation as better than before, but having a (significant) rep limit would be worse than both; I do not give the argument for this general point as it might take the debate off-track.)
There was a minimal rep limit for CW on the old MO (I think 10; the reason for this were posts made in error in CW by first time users).
Already this caused confusion, as I think many did not know this, and some complained at first time posters for not having made their post CW, which in addition to it not being very reasonable in any case, in my opinion; always felt particularly odd if one knew that they did not have the choice.
If there was now a different rep-limit this situation would come back and much worse, as for first time users even not knowing this one detail at least most would think, okay this is a first time user they might not have known, with a different limit this would not be so clear.
So, I am against a (significant) rep limit for making a post in CW. (For current situation or old one I would not care so much, but non-minimal rep limit is worse than both as said.)