I'm putting this into feature requests since I'm not such a big fan of mega threads and mixing discussion with requests:
Problem: With dual_iso being designed to lift shadows, using the original Canon metering doesn't make sense because in a high dr scene the metering will tend to the middle, i.e. clipping both blacks and whites. So with "just" turning on dual_iso you'll get blown highlights unless adding a - ec ... but that will underexpose "alternate frames only".
Suggestion: Add a "Base EC" option (like +/-1/2/3ev) that is only applied for dual_iso shots, thus you can quickly enable it and have "bracketing in one shot" for high dr scenes. The ec would modify aperture/shutter in the usual way just like bracketing does.