My "concern" about this is that queues form at the bio gates.
IRIS is great because it's for regular-ish pax only IIRC (4 times a year minimum?) and everyone gets through quickly (except when you have a divvy in front of you who hasn't registered), bit the bio gates are not to speed the process, but just to reduce staff levels on manned gates.
I don't see why they don't keep IRIS - the investment's been done.