Originally Posted by
subgrade
I'm also tempted to say that the frame is the crucial part. But then I thought about full suspension mountain bikes where the frame consists of several individual parts... is the front triangle or the rear one more important?
Other than the old Cannondale Super V / Ultra V / Raven, which were really just aluminum and carbon versions of the same bike (same geometry) you really can't swap the swingarm between different f/s bikes. The linkage, geometry and hard points are designed together, it's not an assembly that's added on after the fact.
You can change the shock, but that would be like putting upgraded shocks on your VW and calling it an Audi.