Ever since it was announced in the late 60's that King Harald (then Crown Prince) were to marry commoner Sonja Haraldsen, and the heated dicussion of the monarchy's future in Norway ended in the acceptance of their marriage and her becoming their Crown Princess, the trend of both monarchs, heirs and royals marrying commoners has continued and I'm sure it will also in the future. King Harald took the first step, and after them followed many other, and even more will follow. Perhaps we will see some exeptions, but I think the absolute majority of royal weddings in the future will result in more commoners entering the Royal Houses.
So far I think the result is just positive, we've seen wonderful Queens, Princesses and a few Princes entering our beloved Royal Families and it has done a lot of good to them. Great personalities and new faces which have all provided a lot of great things, and perhaps most important of all renewal and modernisation of the old Courts and Royal Households. Perhaps many years from now, when some generations have passed in the Royal Houses, it will become an issue that there is almost no "royal blood" left and perhaps the republicans will use that argument then - but not in these times.
An interesting thing that I've thought about is how the princely, aristocratic and noble families of Europe have continued marry into each other's families, within their own circles, just like the royals did in the old days - but while they've contined, the royal haven't (generally speaking).