I think the thing that will could make HCCI actually work at all speed ranges is the possibility of improved variable-timing valvetrain operation (the next-generation i-VTEC?), which will allow extreme precision in air-fuel mixture control so the compression-ignition process to work throughout the rev range. If Honda succeeds, we maybe talking 30% better fuel economy regardless of engine; that means the current 3.5-liter V-6 engine could get at least 6 mpg improvement in the EPA city cycle! Or the Honda Civic getting 39 mpg in the EPA city cycle....