I doubt it is possible to provide for, even only *Plug/BeagleBoard a kernel
rpms. At least *Plugs use a cut down version of uboot, which only (I did not
see anything else) supports kernel flashing from tftp.
I think it is only possible to achieve the goal of multiple platforms with
setup howto for each pseudoplatform and a base rootfs with bash, tty, ssh,
and other "basic" components plus maybe some package groups like
"guruplug",
"sheevaplug" to enable full support of each devices functionality.
Regards
Bernhard