I've been working on a generic bloodline system that will operate outside of the Birthright setting, and was looking over the Bloodmark ability, which is remarkably weak and does nothing to differentiate the different bloodlines... so I came up with this alternative, which I have only begun testing.

My system uses feats in order to grant the bloodline abilities, some of which are rather power. It also uses the Bloodline (Bld) ability score.

Scion [Bloodline]
You are the descendant of an ancient and powerful bloodline.
Benefit: You gain a subtype, along with certain innate abilities, appropriate to your bloodline.

Bloodlines
Air:You gain the (Air) subtype. You gain a fly speed equal to your base land speed, with perfect maneuverability.

Chaotic: You gain the (Chaotic) subtype. Your natural weapons and weapon attacks act as chaotic-aligned weapons for the purposes of overcoming damage reduction.

Evil: You gain the (Evil) subtype. Your natural weapons and weapon attacks act as evil-aligned weapons for the purposes of overcoming damage reduction.

Earth: You gain the (Earth) subtype. You gain a burrow speed equal to your base land speed.

Fire: You gain the (Fire) subtype. You gain fire immunity.

Good: You gain the (Good) subtype. Your natural weapons and weapon attacks act as good-aligned weapons for the purposes of overcoming damage reduction.

Lawful: You gain the (Lawful) subtype. Your natural weapons and weapon attacks act as lawful-aligned weapons for the purposes of overcoming damage reduction.

Water: You gain the (Water) subtype. You can breathe air and water. You gain a swim speed equal to your base land speed.

Blood Magic [Bloodline]
Prerequisite: The ability to cast 0-level spells.
Benefit: You may opt to use your Bloodline score in place of your normal spellcasting ability score.

Divine Right [Bloodline]
Prerequisite: Bloodline (any) 13+, Strong Bloodline, Leadership.
Benefit: You may add your Bloodline ability score modifier to your Leadership score.

Strong Bloodline [Bloodline]
Prerequisite: Bloodline (any) 13+.
Benefit: You gain a +2 bonus to your Bloodline score. You are immune to ability damage and drain that affects your Bloodline score.

I'm also working on a scion class... whether prestige or core, I'm still working it out... which gains minor spellcasting progression in certain spells that relate to the bloodline, as well as a list of bonus feats available by bloodline.

Any input is welcome.