Hypothetically, it would be cool to make a longer stroke crank to bump up the displacement wouldn't it?!

But there just ain't no room in the case to allow it anyway, so...
(they make the clearances rather tight between the big end of the rod and the inside of the case )

About the only way you could increase the length of the stroke is to make the crank-pin smaller in diameter and move the center point of it further away from the cranks axis of rotation. (off-set grind it )

But you wouldn't get much, without significant loss of strength of the crank-pin. And you'd need to make a new rod, etc. etc.
Maybe make a new crank-pin out of "Nobendium" so it could be significantly smaller? Naw...then you loose bearing area!