The Euro bond idea has been floated around but in order for France to get it the EU would demand they close their deficit in a similar vein to Greece. Like Greece, such a move would be deeply unpopular with the French public. You also got to consider that it is bad enough for a French government to suggest deep cuts in spending but it be a whole lot worse if this pressure was coming from an external institution like the ECB.

In such a scenario I am sure the French government would deather as long as possible and would only comply if the bond markets were getting seriously nervous the French would go bankrupt at which point, and this only a guess by me, they would cave to the EU's fiscal demands. 

The issue here is, as you pointed out, the EU nations are also heavily indebted so a bailout might be hard to stomach by other nations but then if France were to fail they would likely bring down the EU.

If we imagine the other scenario whereby the French were granted access to EU bonds without any conditions then that would also be problematic for the EU. By giving access to the bonds without any/light conditions this would send a big signal to other countries that any kind of financial prudence was not needed as a country would simply apply for EU bonds. If enough countries acted on this assumption then the EU bonds would lose all credibility in the international markets. That would also have dire consequences.

At the end of the day every nation will fall but I think there is merit in attempting to identify the powder kegs that are likely to cause an explosion. To me, while many advanced economies have a shaky debt/fiscal profile it is France that is showing the most red lights. You won't find many countries with a combination of high debt load/high deficit spending/high taxation and a big enough economy to cause serious damage.

Got to remember France is the second biggest economy in the EU with only Germany bigger than it. If the French fall then the EU existence will be called into question.