Although this is cool, the downside is that it only works on specific FPGAs. Are hardware independent designs possible so that one can run it on any sufficiently large FPGA?
But, unlike portable C code, to run designs like this on real hardware, you need to do things like describe how the physical pins on the FPGA are connected to the board peripherals (for instance, describing which pin might be connected to an LED, vs a UART). This generally requires a small amount of glue, and depending on how the project is structured, some amount of Verilog/VHDL code, as well. It's not like saying "cc -O2 foo.c" with your ported C compiler that has a POSIX standard library.
This is just the case if you're using the same base FPGA, but with different board layouts. Using different FPGAs (for example, a current-gen FPGA by vendor XYZ, vs XYZ gen N-1), or especially when porting between vendors -- the details can become vastly more complex very quickly.