Very nice project. Playing with FPGAs can be difficult, but also a lot of fun.
Must say the code was nicely organized and easy to follow. My own code is a bit of a mess in comparison.
Did you try out plain Verilog before going with System Verilog? My plan was to move on to generators like nMigen, now called Amaranth[1], and they spit out Verilog IIRC so decided to learn that for debugging.
Then life happened and got sidetracked, but been wanting to pick it up again.
How was it to program for the Analogue Pocket? I was recently looking at it as just a portable retro gaming device, but if it's easy to double as a fun FPGA platform then that would be great.