Status after more testing. piCore using qemu-kernel from the Raspbian emulator for Windows works on TC 4.6.1 except kernel modules due to the mismatch of kernel versions. Raspbian 2012-07-15 works fine in console mode. Starting X it continously restarts (telinit 5), startx seems to be freezing after the raspberry image, don't know why. Same setup is OK on Windows.
Anyhow, it can be a usable starting for piCore and QEMU variant of piCore kernel.
There are 'pflash write unimplemented command sequence...' errors during boot. There is a patch, applying it this goes away and replaced with more flash related errors, so I didn't apply the patch. Do not know is it related to X problem or not.
Anyhow, it is not for the first version.