According to a reader who recently received a QuickSilver G4, the Read Me for Mac OS 9.2 notes that Mac OS 9.2 supports only hardware that can run Mac OS X. The reader has not tested the accuracy of that claim. However, if true, it implies that Apple has dropped OS 9 development for Macs too old to run OS X.
Similarly, another reader reports that Apple's seeding notes on "Limelight" (the latest code name for OS 9.2, formerly "Moonlight") state: "Limelight supports the same G3 or G4 Macintosh computers supported by Mac OS X." Yet another reader found this quote on Apple's ADC site (on a page that is apparently no longer publicly available): "This update will work only on G3 and G4 based Macintosh computers."
Finally, a reader informs us that the included Mac OS 9.2 Install CD will install on any "compatible" hardware, not just the G4 model that it ships with. This appears different from the norm for other Install CDs - most of which (although not all) are model specific.