The other interesting what-if speculation is, “What if British succession law had changed during Victoria’s reign to give equal rights to her female and male descendants?” Then the monarchs of the UK, and of other Commonwealth countries, would have been:
Her oldest child, Victoria, Princess Royal, who was married to the German Emperor, and whould have reined for about 6 months in 1901.
William II, German Emperor, the Princess Royal’s oldest child, who reigned as German Emperor in 1888-1918, and who would have reigned as King William V of the UK in 1901-1941. Of course, with the personal union of the British and German thrones, it’s hard to imagine World War I having taken place in quite the same way.
Crown Prince William of Germany, who would have been William VI in 1941-1951.
Prince Louis Ferdinand of Prussia, who would have been king in 1951-1994
The two older sons of Louis Ferdinand having renounced their succession rights to the throne of Prussia (though they might not have done this for the British throne), the current monarch might have been:
Princess Marie Cécile of Prussia
Since her son, and her son’s children, are Catholics, they are out of the line of succession, and the Princess of Wales would be her daughter:
Duchess Rixa of Oldenburg
A future Queen Rixa? Sounds pretty cool! (And she is still in line to the British throne, behind 156 others)