I tested PowerMac emulation with qemu-system-ppc

Easy install:
sudo apt-get install qemu-system-ppc

Hard to configure, try find some ready made script+disk image.

I tested with Pinephone Keyboard with mouse, but might run even with N900 almost usable speed, if don't try emulate more than this Powermac 6200 75Mhz with 32MB RAM: http://apple-history.com/6200
and not more than with MacOS 8.1

I only did fast test that it works with Pinephone Keyboard and it would be fun hear Droid4 and N900 tests with different Mac OSs, especially System 7 (might better emulate with SheepShaver) or Mac OSX (would be very slow).

EDIT: It is normal that short time in start it gives some errors about display and keys and is slow to start.
EDIT2: QEMU has two mac machines "mac99" minimum OS is MacOS9.0 so if you try older OS you should choose "g3beige" and oldest OS should be MacOS8.0. So System 7 have to emulate with SheepShaver.