Not to say that there won't be issues, because there always are with new systems, but I don't think it will be that difficult. They will use the bib numbers because that is the only method that makes sense, and the technology is already established. Then, similar to how they give you access to photos at Enchanted Tales with Belle where they don't scan your MB because it would take too long with that many people, you will just get a code (probably via e-mail in this case vs. a card at Enchanted Tales) that gives you access to the photos, and you can enter the code into Disney Photo Pass website to link to your account.
It would be nice if the code was somehow individualized, but if they are trying to simplify it, the code could just give you access to the entire library of race photos (maybe one code for each race) with a bib number/name filtering system similar to Marathon Foto, and you can add whichever photos you want to your download.