If you are on an Intel chipset and you want to implement ACPI based on the ACPI standard and Linux implementation, you will have to use an SMI handler, there is no way whatsoever around this. Well, except writing native drivers for highly mainboard and wiring specific stuff in Linux, in Plan9, in *BSD, in Windows XP, in Windows Vista, in [fill your favourite OS or payload].
Another point on the Intel part, SMM and SMI handlers are also used with Intels vBIOS (VGA Bios) to handle built in drivers for LVDS screens and tv-out chips (they call these modules VBTs and FlexAIMs). I have been doing alot of research in this lately, and it would be great to impliment this into coreboot. That's my 2 cents worth.