How do marginals figure in? If, say, the minimum is 15,000 votes and a guy has, look at that, 15,000 votes, does he get kicked out of the chamber immediately? If not, when? If so, does he come right back as soon as a new person votes for him? What if he hopscotches back and forth? That would make workin very hard, since he'd never know whether he'll have voting privileges or not at any given time. A minor issue, but there's more.
The most obvious way to solve this problem is to have the top X people rather than a threshold. I mean, the chamber only physically has so much space; it'd be better to keep the crowd at a constant size. Timewise, the obvious solution is to reallocate at fixed intervals. It could be a day or a week or a month or whatever. The hopscotchers are going to be the ones with the fewest votes in the chamber anyway, so it shouldn't have that much of an impact anyway.
Second question: Isn't this system vulnerable to opinion swings? Suppose an article comes out that lambasts Rep. So-and-So (who was a very popular guy) for cheating on Mrs. So-and-So. He was working on a bill with a group of other people. Now he loses the votes to pass this bill. Maybe they were working on this a while, and now all of the Parliament sits on its hands until he gets better. Do they start working on a new thing until he gets better? Does that imply a world of alternative laws just floating about, waiting for the number of votes to come in? Isn't this just rule by media? Another issue.
It's a democracy. Vulnerability to mood swings is inherent in the system. There has always been the risk of votes suddenly not forthcoming when public opinion is against it; the first attempt to bail out the banks in 2008-9 failed when Representatives got cold feet after being inundated by angry mail. If a bill fails due to this it only had marginal support anyway, so I'm not worried too much about it. And there have always been phantom bills floating around waiting for their time to come.
Third Question: What about repeal? You said a minority is needed to enact. What is necessary to repeal? Does repeal require the same number? Presumably, then, the number of votes necessary to pass laws would need to be such that there could not exist two seperate-but-opposed blocs can enact and repeal the same law infinitely. Are there limits on repeal? Can the bureaucracy be in the middle of bringing about some law, only for the number of votes needed to repeal fly up because of a single day's unflattering headline? Do they keep working on it? For how long? If it's scrapped, what if the next day, a flattering news cycle leads to it being re-enacted? And related: imagine a Parliament of many single-issue activists. If the law-making barrier is too high, will it be possible to pass laws without making some omnibus bill in order to garner the necessary votes (this is similar to the old Congress habit of "earmarks", but for special issues)? All this leads up to my main point:
How is this parliament supposed to do its business? With members dropping in and out at will, votes going up and down depending on the daily media cycle, laws enacted and repealed at will, it seems very difficult for members to actually work. How is the business of making laws supposed to happen in this stock-market democracy of yours? Where is the power of institution? How would these people handle crisis? Or budgeting? What failsafes are there beyond voters recognizing the issues inherent in the system and acting to prevent them? For some of these, that may be easy, but, say, people deciding to actively avoid changing their votes in budgeting season is unlikely to catch on. There are a lot of questions.
The obvious solution is to require a threshold for passing above 50%. If it's 60% than there are 40% against it and public opinion would have to shift by twenty points to repeal, which seems like it wouldn't happen overnight.
I think the important thing to remember is that politicians are almost infinitely replaceable in this scenario. Let's imagine that Mister A has a horrific scandal and his constituents abandon him. Where they are going to go is to someone very much like Mister A - minus the scandal - and the overall political character of the chamber is unaffected. Votes that backed a Conservative aren't going to fly to a Liberal due to a politician falling away the way they do now. They'll go to another Conservative who will vote nearly identically to Mister A, who can then step into Mister A's shoes.
Another thing to point out is that single-issue activists will be gone. Today, if you have a single issue that is all important to you, you may have to vote for someone who disagrees with you on many other things in order to support that single issue because the number of politicians is very limited for any position. But in a forwarding system, you can choose a politician who agrees with you on almost everything. There would be dozens or even hundreds of potential choices who
all share your views on that single issue you care about and you can shop around for the perfect one.
Crises and budgets would almost have to involve the Executive branch the way they do now. You can't have a situation where nobody proposes a budget or a response to a crisis; that would be a disaster.