I've researched this topic for a while in university, and the idea was to keep a general purpose FPGA as a programming device, and load preconfigured images to it when needed. For example load up an encryption module when encryption intensive operations took place, or load a video encoder/decoder whenever needed.

There were a few problems:

* Each FPGA vendor has its own architecture and such a technology requires momentum from these vendors. A 3rd party cannot do much about it.

* Dedicated ASIC circuits often perform better with less power consumption. So keeping a general purpose FPGA may not bring sufficient benefit to develop the technology.