For the 'blue blood' discussion, it shouldn't be taken as a literal sense. Blue blood means of distinguished discent. Now if for example as will probably happen in Sweden in the case of Crown Princess Victoria's children your grandmother was a translator, your father owns a gym and you marry a commoner then that would put you on a social standing equal to someone coming from a very rich family or upper middle class.
If Victoria marries Daniel and if her eldest child is inheriting, then Swedish people will most probably say: this child is the granddaughter of our beloved Queen Silvia and the heir of our beloved Queen Victoria and nothing else IMHO.
People here who argue with the "lessening of the Blood Royal" as a danger to the monarchy don't understand that it's not the Blood Royal who in reality interests the people (as the voters). Today's still ruling dynasties not only have their history and tradition, much more important is the fact that according to the constitution they in fact sit on top of a country's society. It doesn't matter that queen Silvia was born a commoner - what matters is that according to the constitution of Sweden her daughter is the Crown princess who will one day be the next queen.
Only those ex-ruling dynasties have a need to prove again and again that they are something special and not just people like you and me - which they are in their countries. That's why some branches of the Habsburgs eg are so much against the equality politics of their Head. Because of course it deminishes their prestige. But only because they do not longer rule. Once Mette-Marit became legally the Crown Princess of Norway and the mother of the future queen, she became a Royal in the sense of the Norwegian law.
And those who think that marriages to commoners endanger monarchies do IMHO not understand why there are still monarchies there. Becuase they are a political means to stability. Governments and parliaments of the European monarchies tend to work towards political stability. It's not their aim to have to fight to win elections with the aim towards constructing of a new constitution. They are all quite happy if the things stay as they are.
Thus they have no interest to select their Royals into first and second class Royals according to the bloodlines of these Royals. As I wrote before: the legitimate child of a king or queen regnant is a prince or a princess, no matter where the other parent came from. Legally so and in the eyes of society. And that is why the Royals lasted all those centuries: because they had the power and they ruled. Today the people have the power and the government rules but the people represented by their elected members of parliament decided on the constitution which still garantees the place of the Royals in the society. And for the absolute majority of the people a Royal is who the constitution and the law says is a Royal. The rules are there and most people have no problem with them.
They do have other problems, maybe the amount of money the state spends on the Royals and how much they do in their job. But certainly not a problem with the ancestors as long as the ancestor held the staus and position of a member of the Royal family in his or her life. Diana never was a Royal herself due to her descent, but she still is called by many "Princess Diana" even though she was only ever "The Princess Charles" wehn it comes to first names. Does it matter? William was born as the son of TRH The Prince and Princess of Wales and thus he is a prince. If he marries Catherine and they have children together they will be born the children of TRH The Prince and Princess William of Wales and be granted the right to be called Royal Highnesses and Prince/Princess as well. No matter if their mother was born Miss Middleton. I doubt many people will think about that fact and probably only when they see the baptising pics showing the grandparents Middleton.
Or did anyone have problems back then in a quite different time, 50 years pre-French revolution when Louise-Elisabeth de Bourbon-Orleans married the king of Spain? Who was interested that her grandmother on her mother's side was just the lover of her grandfather Louis XIV. and not a princess and not married to the father of her daughter? So if the Royals back then did not bother too much about bloodlines and the Royals of today do neither, and if the majority of the people are only interested in the fact if the new bride fits in with their expectations of a Royal bride - then who should kick the Royals with "too much commoner blood" out of their august position?