It's not like there's only three days left until the con and I decide to come up with a new product and now I'm attempting to mass-produce it by myself 
Silly, I don't do things like that! 
Ficcer instincts are trying to get the best of me · 10:51pm Sep 19th, 2012
I'm really actually almost considering writing the damn Discord/Celestia fic I have in my mind. But I know I shouldn't give in since I haven't managed to finish any story in years so chances are that I'd start this, maybe write a couple of chapters and then abandon it 
It doesn't help that this would be a real epic, seriously have anything between 10 and 20 chapters. Ugh, and it has some very used ideas in it that I'd feel a little guilty for using since it'd be unoriginal (I feel fine using them in my headfic that's only for my personal entertainment, but not in something that'd be for everyone to read). And it'd be the first long English fic I have done (since in my mind it is in English, I can't suddenly make it Finnish anymore) so that'd make it even more challenging.
Get out of my head you plot bunnies who insist on making me write 
You know, you could always just write it for your own entertainment/sanity and have it on your personal computer, then maybe if it ever gets to a point where you think it's good enough (and you're far enough ahead) then you could start posting it if you wanted.
I struggle with the whole 'used ideas' thing as well. There's a few things that I really, really, really wanna do but every time I think of them I see at least two other stories similar to that. I guess my only edge is that I could try and put my own spin on it, than maybe the readers would like my interpretation.
That's one reason why my head-canon doesn't contain DisLestia, with one fell swoop of a sentence I eliminated that from the readers' expectations (that doesn't mean that I don't like DisLestia, cause I do. Just decided to put my own spin on their relationship to better suit my story).
What you have to remember is that no idea is truly original. Sadly the human mind is limited in even its capacity to imagine most of the time, mostly because we all have the same source material here (in this case FiM) to work with. A few people may look at the source and characters and come up with the same or similar ideas as you based on the fact that they just might see it/them through a similar pane. I really hate to think that people might think I'm unoriginal, or that I'm 'copying' someone else (another reason I try and stay away from other DiscoLight stories). Eventually though - if it's a story you really wanna tell - I guess you just have to suck it up and write it, be fearless. I say that as much for me as you.
Maybe an outline first would help, or starting as close to the end as possible. Or just start doing scenes and thread them together later. Do the juicy parts first.