I expect they moved away from this because over the large population trial they discovered cataracts can interfere with the accuracy of an iris or retina biometric system and an iris scanner will not work with patterned or coloured contact lenses, which are changeable.
Some good info from Oz
What You Don't Know About Iris Recognition -.
Facial recognition still seems to have difficulties with ethnicity so that is probably why for the time being fingerprinting is still the best option.
Ooh nasty, was that from peripheral neuropathy?
Only works on people called Iris, unfortunately.
Or Bond, James Bond with his Aunty Iris’s iris implant.
Iris Recognition, that was my mother-in-laws name.
He has that as well, but the fingerprints went first, quite early in the 6 month chemo cycle. He found out when his iphone wouldn’t open! Facial recognition no good either.
I was on fulfox 5fu, but they cut one possibly oxaliplatin when I got perpheral neuropathy thankfully before any further damage was done it was around 6-8 cycles.
Always helpful to read the actual legal text, to back up the guides… And any person with a CDS or a Brexit legal resident in the EU, who is (incorrectly) entered into the system will, after 90 days, have an ‘overstay’ logged, and probably be denied entry next time they take a trip. So not all TCN’s to ‘pass through’. Also it’s not just ‘gates’ - I understand scanning will be at booths which people walk up to and scan themselves - the entry then logged at the passport desks - or possibly automated booths.
So TCN’s outside of the system will not do initial scanning and will present at the desks with cards or their Brexit exemption proof? Which could be fun for e.g. Spanish residents who weren’t issued cards.
The legal text -
REGULATION (EU) 2017/2226 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL
of 30 November 2017
establishing an Entry/Exit System (EES) to register entry and exit data and refusal of entry data of third-country nationals crossing the external borders of the Member States and determining the conditions for access to the EES for law enforcement purposes, and amending the Convention implementing the Schengen Agreement and Regulations (EC) No 767/2008 and (EU) No 1077/2011
Article 2
Scope
(c) holders of residence permits referred to in point 16 of Article 2 of Regulation (EU) 2016/399 other than those covered by points (a) and (b) of this paragraph;
And here’s the clause excluding those EU member states which have not issued Brexit permits (the ‘declarative’ system where those meeting the conditions required automatically have rights under the Withdrawal Agreement) - these countries are Bulgaria, Croatia, Cyprus, Czechia, Estonia, Germany, Greece, Italy, Ireland, Lithuania, Poland, Portugal, Spain and Slovakia.
(a) are members of the family of a Union citizen to whom Directive 2004/38/EC applies or of a national of a third country enjoying the right of free movement equivalent to that of Union citizens under an agreement between the Union and its Member States, on the one hand, and a third country, on the other; and
(b) do not hold a residence card pursuant to Directive 2004/38/EC or a residence permit pursuant to Regulation (EC) No 1030/2002.
Safer to stay at home methinks. Can’t be ar*ed with all this carry on. You can understand why french folks like to remain in their own country in the holidays and now I read that the spanish islands and mainland are protesting about too many tourists and second home owners - wouldn’t want to be going to any of them this summer.
If I could everywhere by car, I would, but there are some places only accessible by boat or plane - sounds like it is going to be a right faff when it starts up.
The EES will still monitor UK nationals with France CdS and WARP TdS to control the 90/180 limit spent in another EU country that is not France.
In addition, France needs to keep record of CdS and TdS holders’ time out of France, both to verify residency and to uphold the limit regarding absence from France. The CdS or TdS issued to UK nationals is a residency permit for France, not for all EU and does not carry the same authorisation as a French carte d’identity.
To cover the new border monitoring, France and each EU country will be on one system.
Show passport + show CdS at France borders + electronic fingerprints. There will be no need for stamps in passports as tech has moved to fingerprints. There will be a need for fingerprints until the print records on France’s CdS system links into the EU EES system. That may take some time, if ever.
Anyone travelling imminently should be prepared at an EU border to be entered into the EES fingerprinting system. UK nationals with CdS included. You may be pleasantly surprised!
Judging by the M20 and tunnel road links they are not expecting it to be sooth.
This, latest from Connexion
States:
It will see non-EU travellers (with the exception of residency card and visa holders) entering the Schengen area required to provide biometric data, including fingerprints and a photo of their face, before they can travel into the bloc.
However, in the initial confusion of the first few months this autumn it may be best to be prepared for whatever is officially requested while at the border and not to demonstrate angry arrogant foreigner syndrome.
Almost got my passport stamped at Beziers airport this morning. I had to verbally ask the douane officer not to stamp it as she had my CdS in her other hand 
. Luckily, didn’t get strip searched for my impertinence. She was actually very apologetic, as she was distracted talking to another officer next to her.
My wife came through the Chunnel this morning, the French PAF at Folkestone were all smiles and said that her CDS was enough for them, they didn’t even bother with the passport.
A work colleague of mine learnt the hard way about being impertinent to customs officials. We were travelling to the US, he was questioned, was rather cocky and next thing he’s being treated to the James Herriot rubber glove treatment - certainly wiped the smile off his face! That was a few years ago now, so wonder how that treatment would be possible in today’s hypersensitive world.
In my experience (not that I’ve ever had the rubber glove treatment), US border guards are impervious to the hypersensitivities of today’s world when they are deciding whether to let you in.
Yes I’ve always found the first point of contact with the US on arriving to be a tad impersonal and somewhat hard. Once out of the airport that soon changes, with ‘have a good day’ being thrown around like confetti 
I used to quite enjoy entering the US on my A2 visa as they didn’t so much as ask a question.
Never mess with US customs! I learnt that as a cheeky 16 yr old. Never forgotten.