I'm not sure if I could stand to port it without rewriting the janky bits... But a straight port should actually be pretty easy, just retarget the pin mapping and figure out the magic for the PLL block configuration... ECP5 is basically a superset of ICE40 in every way so I don't think synthesis would break a sweat.
I don't have the bits and pieces to hook up output on my ECP5 board, but lemme see if I can bang yosys into producing a bitstream...