It's question of whether we are willing to do unthinkable,
i.e. to break QEMU <-> guest ABI for isapc case by removing
corresponding fwcfg entries.
It's not unthinkable since it's unversioned.
we are loosing a chance to cleanup
QEMU code base touching following 
    m->option_rom_has_mr = true;                      
    m->rom_file_has_mr = false;                           
    pcmc->pci_enabled = false;                            
    pcmc->has_acpi_build = false;                      
    pcmc->smbios_defaults = false;                    
    pcmc->gigabyte_align = false;                            pcmc->smbios_legacy_mode = true;                  pcmc->has_reserved_memory = false;
Some of these can go away, for the others probably we can think of making isapc a direct subclass of X86MachineState.
I would rather keep it because it's the only way to test userspace interrupt injection in KVM.
Paolo
they are all marginal but in shared code, and removing them
makes code a bit more easier to follow (especially when it
comes to memory layout).
> With regards,
> Daniel