Any single Rep can call for a 'no confidence' vote of the Speaker.... (It used to take such a call from the leadership caucus, an unlikely scenario.)

No, it didn't "used to." Any Representative could call for a move to vacate from Congress' inception. It just didn't happen very often (Boehner being the last, and he avoided it by resigning in lieu of the threat of one). It was the Pelosi regime that imposed the limited and protective leadership caucus requirement. All the "new" rule does is restore the status quo ante. The greater risk is that members of the Progressive-Democratic Party will frequently move to vacate. In the event, though, moves by any member would only present a disruptive day or two, since the motion must immediately go to a floor vote.

...roiled the markets, causing stocks to plummet....

There's a big so what. The markets aren't the economy in which average Americans live and work and spend. The markets are tied to our economy with a thick, stout rope, but there's a tremendous amount of slack in the rope due to the lack of temporal connection between the two--there's just too much time variability in the feedback loop among actual doings in the economy, government machinations with spending and taxing, and investors' and traders' actions in the markets.

Regarding the debt ceiling raise, it's been too often and too easily raised in order to support the borrowing (which is the real risk to our national credit rating) that Party politicians, Republicans who agree with profligate spending, and Republicans without the courage of their own convictions and so go along to get along inflict with their profligate spending. In the event of a government shutdown, tax requirements would continue, tax revenues would continue to flow, and interest on the national debt would continue to be paid--no default, although that is a technicality.

What has happened in the past is that blocking the debt ceiling raise was used to force concessions on future spending so as to obviate the need for future ceiling raises--only to see those agreements welched on by the big spenders. Hopefully, the current crop will be made of sterner stuff and the agreements regarding future spending will last longer.

Interesting that unions are allowed to threaten a business' existence altogether by blocking its ability to produce with strikes, but politicians aren't allowed to insist on fiscal responsibility in our government.

Eric Hines