Assuming my previous theory on the balance between races is true (i.e. that the loss of laguz nature is a matter of balancing unequal power distribution), it's possible the odd abilities associated with Branded - great strength, superior magic ability, Sacrifice, ability to hear Ashera and sing galdrar - are close enough to laguz abilities to create some kind of cosmic equality. Perhaps not in every case, but someone like Micaiah, who possesses most (if not all) of her laguz progenitor's abilities, is really only lacking in wings and the ability to transform.
The jury is out on whether this re-balancing would involve just the laguz blood (and therefore include carriers like Sanaki), or if it requires a certain strength of inheritance, or if the Brand would be the deciding factor.
2. Mark of the Apostle = divine interference
My impression was that brands appear randomly, and usually when the carrier is a child. We don't know very much about this, but if there were any consistency in the way it came down the bloodline, people like Zelgius would have some clue regarding their eventual er, tragedy.
The Apostles, however, were always firstborn children. There's no information on whether or not the mark went to every single generation, or if it skipped. I'm thinking it didn't, because thirty-seven empresses in an 800 year period makes it sound pretty consistent. If other brands act differently, it suggests some interference. Since both Yune and Ashera show some ability to hit Micaiah with their foresight even while asleep, it's not out of the realm of possibility. They don't have to be aware of what it is to shift the probability of the ability to awaken them.
3. The dragon and bird tribes can mate
Surely they can. I'm thinking of dinosaurs being the ancestors of avians. :D :D :D Okay, this isn't a real theory, it just amuses me.
4. It'll take a hell of a long time to restore the heron clan
Given Ena's 15-20 year pregnancy, and assuming it implies longer pregnancies for longer-lived races (and it's already implied their childhood stages are stretched out), I'm guessing Leanne will only have kids once every twenty or twenty-five years - and that's if Naesala is diligent. He probably will be. But Leanne will need to take a break eventually.
That really sucks for Leanne. XD However, it might be possible that a mix of the bloodlines - in this case, raven and heron - will modify that time period. Ravens probably have slightly faster pregnancies, seeing as they live on average what, only five to seven hundred years? >_> Herons obviously live longer, unless Lehran is just strange - and I have a theory for that, but it's stupid, and only belongs in fic.