On my first skim through I missed the fact that Elven Blooded isn’t a general proficiency and so figured that an Explorer with alertness and elven blood would make a good wood elf Legolas type, simply assuming that the proportion of his blood that was elven = 100%.
Looking over it, explorers don’t seem to have access to elven blooded unlike mages and bards. It seemed like a natural fit to me so now my curiosity is piqued, how come it isn’t on the explorers list?
[BTW I am really impressed with what I’ve seen so far.]
This isn’t an answer (because I don’t know), but I thought I’d let you know, if you didn’t already, that there’s going to be a full-on Elven Ranger class in the Players Companion. So that’s something to look forward to.
Each class has a limited pool of proficiencies. The exact formula is listed in the Player's Companion. In any event, I simply selected proficiencies I thought were balanced and diverse across all the character classes.
Nothing particularly "breaks" if you let an Explorer take Elven Bloodline, but you should probably take away one of their other quite useful proficiencies in exchange.
As Ludanto said, there's an Elven Ranger in Player's Companion that might be a good fit, too.