it was my understanding that the reason the pcmcia/cardbus stuff got integrated into kernel in the first place was to support booting from such devices.
I believe you are correct but I seem to remember that it will only be posible via early userspace due to the database lookup cardmgr has to do.
I just did a test with my adapter. I compiled bot the bridge driver and the ide-cs into my 2.6.10 kernel, moved cardmgr to cardmgr.norun and re-booted. The bridge was found but the ide-cs device was not. Running /sbin/cardmgr.norun by hand enabled the ide-cs like normal. So looks to me like its still dependent on cardmgr.