Yeah there's really so much I can do there as far as changing up the filled holes. There may actually be something to work with in the recently updated engine but I haven't dug into it yet (it builds down to Mapper 2 instead of Mapper 0 so I would have to rewrite all of my engine hacks from scratch). I'm also considering making a sequel in NESMaker, someone built a Sokoban puzzle patch into the Zelda-like adventure module and I could do some wild stuff with that I'd imagine.
But yeah I'm also pretty obsessed with fonts. This one took months to fine-tune.