I doubt that will be a problem as I don't get the impression that Skyrim has hair physics, which doesn't really make very long hair more doable, in fact, I'd imagine that the lack of hair physics in Oblivion was the main reason that hair longer than shoulder length wasn't possible, because since the hair would just be completely rigid, it would very easily cause clipping issues.
...and it did, which is why I've always skipped the various long hairstyles in the hair mods I've tried. Having your hair sticking through your shoulders or out of your chest (when crouched) looked really silly.
If hair can draqe and animate in Skyrim, long styles might work. Otherwise....... :shrug:
Does anyone know if your hair will grow in time?
God, I'd hope not. If I go through the trouble to design my character's look just the way I want it (including hairstyle), I'd hope that it wouldn't mutate on me.