(WARNING:Really farfetched and crazy theory) Don't take it personaly its just one person's opinion emphasis on OPINION!!!
Ok ok ok ok...
I'm just going out on a limb with this one but, There is alot of controversy with Scootaloo being a disabled flyer and her idolization with Rainbow Dash so here is my twisted outcome as to what COULD happen to her.
For starters if she happens to be the last Filly to get her cutie mark she is going to feel extremely left out and alienated from the rest, which in return is not going to benefit her mentally or physicaly. Its allready looking pretty grim since both Sweetie Belle & Apple Bloom both have sisters that they can fall back on when there is trouble. Poor Scootaloo on the other hand from what I've seen on the show has no one WHERE ARE HER PARENTS?! Let alone any relative or guardian for that matter and sure Rainbow Dash took her in as a "sister" figure but in ways she is busy with her various tasks (what ever those may be) and can't be there for her all the time plain and simple Scootaloo is by her lonesome which could cause her to loose grasp with reality basically slowly deteriorating like Pinky Pie did in "Party of One" creating fictional freinds all that good stuff not to mention what all the other Ponies would think of her after her descend into madness. Now for the biggest one of all her inability to fly I'm pretty sure everyone has experienced some point in there life wanting something they can't have or its just out of reach taunting you relentlessly she has gotta be heart broken knowing that she is never gonna know what its like to TRULY fly with her Hero forced to look up in the sky as Rainbow Dash slowly fades from her sight feeling useless wondering if she will ever see her again. There is a chance however that Rainbow Dash can help her being the Element of Loyalty and what not. There is the thought of Scootaloo becoming a deranged stalker too following Rainbow Dash every where she goes (to the best of her abilities) keeping tabs on her, snapping photos... the works!! Scootaloo has an unfortuante fate ahead of her that only Rainbow Dash can fix. One can only hope that Rainbow Dash isn't going to let her down!