As you can read on AppleInsider, the PPC support seems to go away from Mac OS X 10.7. I don't expect Apple to ship Xcode with PPC support for Lion.
This means that once I move to Mac OS X 10.7 for developing plugins, I will drop PowerPC support. That will likely be as soon as the GM version is available (maybe two weeks before official launch). Whether Mac OS X 10.4 support has to end the same day, depends on whether I can configure compilers to output plugin libraries which still load on Tiger.