It seems to me that the problem (if it is a problem) we have here is somewhat complex and confused by the fact that although there is a specific title available for the wife of a male monarch, there is no specific title for the husband of a female monarch.
In my opinion, a monarch whether male or female should be considered of equal status and it follows therefore that the spouse (whether male or female) of a monarch should be considered of equal status too. As such, Daniel Westling once he married Victoria, should be accorded the same status as, for example, the wife of Crown Prince Frederik of Denmark. However, because custom, tradition, precedent etc throughout history enables a female to take on her husband's title but not vice-versa, there has never been a title/name available or created specifically for people in the positions that Daniel Westling, Prince Henrik, Clause Von Amsberg or the Duke of Edinburgh are in.
It would seem odd (though I'm not entirely sure why) if Daniel Westling were given the title Crown Prince, because that title has always been associated with someone who is next in line to the throne. It would seem even more odd if, when Victoria becomes Queen of Sweden, Daniel becomes King of Sweden.
To my rather confused mind, the bottom line is that in reality, there is one meaning for the word KING and two meanings for the word QUEEN (royal related!). The rank and status of the title QUEEN depends on the office the bearer of such title holds.
With regard to equal primogeniture, clearly whatever system of succession is used, there will always be some kind of inequality about it. The system of monarchy (and most forms of state institutions) is by its very nature and history not one based entirely on equality.