Specialized coprocessors are super common but they're basically all ASICs with nary an FPGA to be found. In theory you could have reconfigurable co-processors on a mainstream chip but nobody does that - partially because the latency involved in reconfiguring the FPGA makes it a losing proposition in most cases.

There are uses for FPGAs where there's enough money at stake for the hardware development but the number of units is small - stuff like high frequency trading or many defense roles. Or in the development of new hardware. But it's pretty niche.