Dynasties could bring back 'Permanent Alliances' ?

  I would like to have a way to obtain permanent alliances once again.  I figured a marriage between two peoples would be considered one of the stronger types of alliances that could bring this about.  Can't stand it when I go through early and 1/2 mid game researching the proper techs to get treaties/alliances & such only to be limited to a 100 turn max partnership (& that's only if I have someone close enough that's inclined to buddy up with me).  This would also add another significant importance to marrying your daughter off (lets hope you get a daughter as perhaps this would be the sex needed) rather than just doin it for tha children.

  Or maybe Selectable Sov traits could bring this into play.