I'm pretty sure that in theory, probably just about anything you wanted- the problem here is that you'd need to develop a Mac OS driver for each feature (and in some cases, develop an entire stack to support features that had no equivalent, i.e. USB, on classic Mac)
Also to clarify, K55 who started this thread was working to make a more accessible Mac-ready hardware kit using the schematics developed by kugimoto0715 (
http://www.geocities.jp/kugimoto0715/), I don't think K55 or anyone else here has actually progressed down this route much further- I was originally interested (and have to return to the topic) in using the project to create a multi-game Apple/Bandai/Atmark Pippin game jukebox, as the SCSI2SD has some limitations to this regard that make implementation a bit difficult, but I haven't done any more investigation.
On the topic of drivers, kugimoto0715 provides two drivers similar to what you're referring, but for x68000 (one that allows remote file system access, and one that allows the Pi's ethernet to be used directly, but both appear to have been developed through a mixture of already existing software to allow emulators to access their host os.
I might look into an updated technically accurate re-translation of the page if no one's poked at it recently, as I see there's some updates since it first went live (I've also seen the compatible adapters for sale in shops such as BEEP recently, so it's no surprise that it's been gaining momentum). curious what this initiator and monitor mode options offer...