Well, 2 historians used this quote in their books so I considered that it would be interesting. This quote is not the single argument in favor of the possibility of a victorious intervention. The following informations come from the book "the great defeat 1870-1871" of Alain Gouttman.
Battle of sadowa happened on July the 3rd. The 4th, the austrian ambassador Metternich called france for help.
The next day, a day that numerous authors considere as "the most decisive of the second empire", Napoléon III is with his principals ministers to decide if France must intervene or not. Several french officials was ready to intervene. The minister of foreign affairs, the minister of war and Eugénie wanted an intervention. Napoléon III hesitated as usual.
The maréchal Randon (minister of war) told, not exagerating, to the government that he could concentrate 80000 men in Strasbourg at this moment and 250000 in 3 weeks.
The minister of foreign affairs even told "40000 is enough!".
Bismarck told to the parliament in 1874 that "Even if France had not so much troops at this moment, the addition of a few french regiments would have been enough to transform the important troops of South Germany, who had an excellent equipment but without organisation, into a very good army who would have immediately forced us to cover Berlin and give up to all of our successes in Bohemia.".
Benedetti, french ambassador, was sent in emergency to Bismarck in Bohemia, in the middle of the staff. The french told him to not forget the armistice asked by Vienna. Bismarck answered that an immediate armistice was too kind to Austria and that "Today, the way to Vienna is open. In 3 days, it will be closed".
It was admit, without telling it, that the Sadowa's victory was not as complete as the Great prussian Staff had wanted: conceived like an obliteration battle, it only have been a repelling of the enemy without preventing him to continue the fight.
July the 12th, Austria again called Napoléon III for help, the emperor didn't reacted.
Even with the best troops in Mexico and the problem of money in military administration, in 1866, the French imperial army remained an intimidating force. Beust (austrian diplomat) -like Bismarck- was right to think that a simple show as the sent of an observation corps on the border would have been enough to fear Berlin.
The austrian diplomat reported that he told to Napoléon on July the 12th: "Majesty, you have one hundred thousands of men in Châlons. Move them to the border. The operation's line of the prussian army is already too large so this army will must be forced to stop. In Vienna, Munich and Stuttgart, we are regaining courage and Germany will welcome you as a mediator. Otherwise, be careful, it's all of Germany that will be made against you.".
I finished the quotes. Finally, it seemed to me that the question of the possibility of a french intervention is not settled.