A most interesting turn for colonial development, I must say
I still haven't found my Great Fixation, although I do have a list of candidates. It's been far too long since I've found an idea and fixated on it to the point of obsession. In fact, I think the last one was my quest in your Tuscan/Byzantine AAR when I kept pushing you to take on the Ottomans
Anyway, the list:
1.
Unify the Iberian Peninsula
Pros: You're already 2/3rds of the way there, and it can be called the most historically plausible option
Cons: Too predictable for my tastes, and likely to be too easy
2.
Unify all of Italy
Pros: Again you're already a good portion of the way there, and Aragon had a historical interest in the Peninsula
Cons: As above, with the added negative that you might get on the Pope's bad side
3.
Recreate the Western Roman Empire, at least territory-wise
Pros: Combines 1 and 2, plus gives you a nice, large empire to play with
Cons: That "nice, large empire" will be insane to manage, the enemies you'll make in the attempt will be significant (France, England, the Pope, and that's just the guys in your direct line of conquest...), and still a bit too "standard" for me...
4.
Conquer All Africa
Pros: A nice challenge, you've already started, and just "out in left field" enough to interest me without being totally impractical--probably my favorite idea of the bunch
Cons: Time, resources, slight possibility of getting on the bad side of a large and important chunk of the Muslim world
But, as I said before, I'm still narrowing it down, although, as noted above, the "Conquer All Africa" one is becoming a fast favorite. Also feel free to refer to this post as a tipsheet for some of your own plans, should you choose to do so