Maybe. Depends
on what "does not fit" means here. 
 [...]
> If it means "critical pieces of the design cannot be implemented in
> FPGA at all", [...] 
 
  I'm not sure what kind of problem you're
trying to describe here.
 Can you give an example? 
For example, if a critical piece of the design is analog electronics,
not digital at all.  As a really simple example, it involve a D/A or
A/D converter.
/~\ The ASCII                             Mouse
\ / Ribbon Campaign
 X  Against HTML                mouse at 
rodents-montreal.org
/ \ Email!           7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B