this is just a test with boot yosemite OSX 10.10 with last amd kernel rc7 of Bronya.
It's a crazy idea of mine, to use the system driver data or even folders from 10.9.4, maybe that's a start on which we can build on it. I'm just now doing upload the video
The experiment can test each.
proceed as follows:
1) Install Yosemite OS X 10.10. on your USB Stick,.... there are many examples on how to do that.
2) copy the following System drivers from 10.9.4: "AppleACPIPlatform.kext, Corecrypto.kext, IOACPIFamily.kext, IONDRVSupport, IOPCIFamily.kext, IOUSBFamily.kext, Sandbox.kext, System.kext" and then paste the System drivers into Yosemite OS X 10.10 /System/Library/Extensions/
3) copy the "Core Services" folder from your Mavericks USB install Stick ( 10.9.2 or a different Version), then paste into /System/Library/
4) after you have made all these things, use Kext Wizard, repair the permissions and make an Extensions.mkext and add it to /System/Library/
5) use the last amd mach_kernel_rc7_fix (for FX or older amd CPUs) of Bronya and paste it into the root directory, then the bboot from the USB Stick
what I've found is that Yosemite can boot only with insert of "Core Services" folder from 10.9.4 or a different Version, then yosemite can boot with amd kernel.
hence is a file in "Core Services" which must be the cause! here has to be found out which file is the prevented the boot.
I suspect the boot.efi
I'll test with original "Core Services" with bootefi from 10.9.4 and will report without success, there must be something else
sorry for the quality, the original recording is about 1 GB in size and requires a lot of time to upload, which is a converted version with about 20 mb