He cut Cloud, Leon and the gang not because of lack of space but because, as you said, there would be too many characters in one world. That's not going to change in an international release. There are still more than enough characters in Radiant Garden, and adding more would tip the scale too far.
Let's look at what they added to the KH1 international release:
- Sephiroth
- Ice Titan
- Kurt Zisa
- Phantom
4 bosses. If the same were to be done for BbS, with the 4 same categories, it would be:
- Sephiroth/Some other Final Fantasy character. But with Cloud younger and in RG, there's a strong chance Sephiroth doesn't even exist at this point. And, as you said, if Cloud isn't in the game (and I've given my reason as to why they wouldn't add him), Sephiroth wouldn't be anyway. Instead, if it were to be some other Final Fantasy character, my bets would be on Genesis. Stop and think about that. They had Cloud in the Japanese KH1 and added the primary antagonist of FF7 in the international release. And for BbS, they have Zack, the primary protagonist of Crisis Core.
- Wind/Lava Titan.
- Random Unversed optional boss.
- Random Unversed optional boss.
Though I would prefer something other than random Unversed bosses. After all, we already have Iron Prisoner and Mimic Master, two optional bosses in Mirage Arena. So if I had to choose two other bosses, it'd be the Hag/Evil Queen and an Armored Lingering Sentiment of Master Eraqus. I doubt they'd add the hag since they'd have to expand the story for that world, but it was really
the biggest waste of an opportunity in the KH series. Months ago, having a boss fight with the Queen wasn't even a question for me, it was just so "obvious" that it would happen.
And then for Eraqus... I just want an excuse to see him fully armored.