You clearly have a challenging definition 
. Unfortunately, full compliance would, in most cases, result in prolonged periods of no government whatsoever (frequent elections + PR + 50% vote requirement to establish a government - unless the country is as homogenous as a single rural Norwegian province, this is a recipe for a disaster). In fact, I would conjecture, that a fairly democratic country in your definition wouldn't have a government most of the time . Furthermore, who forms the government - when this actually happens - would, most of the time, be determined not by by the voter preferences but either by chance or by some unelected authority, such as an electoral commission (there are, in fact, very solid theoretical grounds why that's would be the case).
Because what you are describing is (for a bunch of theoretical reasons) bound to be extremely manipulable and dependent on all sorts of minor decisions by everyone and their grandmother. Basically, when no government can be formed subject to you constraints (that is, most of the time), something has to occur, and that something will be rather random, dependent on things you'd consider minor technicalities. Since the electoral commission has a key role in making technical decisions, de facto, most of the time it will be the commission that wil ldecide who rules without any reference to the voter will. In reality, the country will be ruled by unelected bureaucracy, since the elected representatives will be incapable of ruling. It won't exactly look like that, but that is what will really happen.
By the way, the country will only be stable if it has strong and legitimate bureaucracy. Few countries will remain stable under the circumstances.
