ReactOS r74613 doesn't boot when using QEMU's more modern Q35 platform. It fails early with an IO1_INITIALIZATION_FAILED bugcheck.
Minimal example that triggers this bug:
qemu-system-x86_64.exe -M q35 -cdrom bootcd.iso -serial file:CON
I'm using the Windows build of QEMU 2.8 (2.8.50 (v2.8.0-11974-g0511122345-dirty). Debug log is attached.
Booting this minimal example using the traditional i440FX platform (-M pc) works.