What do you think most popular usage of FPGA?

I doubt it. Not many people make ASICS, and while they make use lots of FPGAs for a single ASIC prototype, they won't use a continuous stream of FPGAs.

Lots of companies make industrial equipment that sell 100s or 1000s of units a year that each have an FPGA. FPGAs can often be used when you want an initial release and add features over time, or be able to customise units to customer demands.