Update: It boots, and KEXEC works :-)

X didn't start, but that's probably something wrong with my build. The console works, but fn doesn't which means some essential characters like / can't be entered. So I couldn't try to configure WiFi, bluetooth etc and see how they worked.

If anyone wants to give it a go, there are some steps omitted in the above link. Before menuconfig copy feeds.conf.default to feeds.conf (and optionally edit it to enable package feeds of interest). Then run "./scripts/feeds update" followed by "./scripts/feeds install xserver-xorg" (and whataver other packages you want to include - use "./scripts/feeds list" to see what's available).

It's possible you may also have to run "make tools/install" if the build fails complaining it couldn't find some host-side tool.

If all goes well the results of the build will be in bin/omap24xx. You don't really need to flash the kernel, a simple "flasher-3.5 -k bin/omap24xx/openwrt-omap24xx-zImage -l -b" will do for trying it out.