I was actually always a big proponent for a very similar idea before Alleria's return. Just like you say, I thought Alleria becoming a Fel-infused "blood elf" in her fight against the Legion would be an interesting way to perhaps compel some reflection in the youngest Windrunner sister. I had also hoped she might act as a mediator for further reconciliation between all the "Children of Silvermoon" as Auric refers to all Thalassians elves, maybe even becoming a member of a newly reformed Convocation of Silvermoon.
But, alas, the introduction of void elves took Alleria down a different path. There's still lots of interesting opportunities to be had from the development of the Ren'dorei story and Alleria could still be the one to bridge the divide. Just not on the Isle of Quel'Danas or anything! ^^'
I'd like to hear more of Vereesa's opinion of Alleria and her acolytes though! It must go against the grain for her to have another sister use such potentially dangerous magics and lead a following of former blood elves (and maybe high elves) who do the same.
I would wholeheartedly agree with you on both fronts. The divide does make things a lot more interesting and complex regarding Thalassian lore. You don't anywhere near the same depth of tension when discussing Bloodhoof and Grimtotem tauren or Bronzebeard and Dark Iron dwarves. We Thalassian fans, whether we carry a red or blue banner (or both) are fortunate to be able to have such heated discussions!
And, oh, how I have longed for Farstrider tattoos for so long!