Now an OS can have a standard driver and use it to activate hotplug functionality. This is OS hotplug (OSHP).
So presumably this will work on targets that don't have ACPI? Assuming a competent guest OS of course. Have you tested this?
This being the qemu side of things? I run Linux and verified that it calls OSHP and afterwards, runs the native driver and handles hotplug/unplug without invoking ACPI at all.
I mean using your shiny new hotplug PCI-PCI bridge on arm/ppc/mips targets (i.e anything other than x86 PC). From your description it sounds like it *should* work.
It seems that at least the SHPC driver in linux doesn't work if you don't have an acpi table with the OSHP method - not many people run with acpi=off nowdays, so it's probably just a bug. I'll check how hard it is to fix this.
Targets other than x86 don't have ACPI to start with.