Yes, yes you should write a Xiu Min fanfic. I already started on mine, but it doesn't solely focus on him. It's a family fic you see, so it changes from his sister to him from time to time. Well, it doesn't matter now... cuz I put it up on *sniff* hiatus *sniff* because I just couldn't bring myself to type it out anymore!! Even if I've already planned out the ending... the words just won't flow! It's unnerving...
Anyways... wow... I blabbed. Okay... By the way, back to the question. If you feel like you want to write a Xiumin fanfic, then go on ahead... It's your choice~ ^^