Yes, one button to indicate a fill, and another button for which one. Particularly Intros, you've always got enough time that pushing two buttons isn't a problem, and them being next to each other helps. Endings, you just get used to it.

But think about it for a minute... Four Intros, and Four Endings, Four variations, seven fills, and you want DIRECT control over each of them? That's a bank of NINETEEN buttons! IMO, that's would be easier to hit the wrong one than the system they have now!

As to the fills issue... Well, more is ALWAYS better (unless it's weight!), but it more goes to the number of variations. Two fills (one UP one DOWN) works great for a two variation arranger. The fill up is going from one place to another, and it's always the same. But a fill UP on a four variation arranger might need to go from a gentle Var1 to a slightly less gentle Var2, OR, it might need to go from a gentle Var1 to a busy Var4. Same (even more importantly, actually) on the way down.

It just makes for more natural musical transitions, and most importantly, less repetition (the bane of arrangers!).

Korg's are very good arrangers, but this ONE aspect is still mired in the 80's, compared to their competitors.