Or, would passengers prefer less seats, wider aisles, and grab rails? There may, especially on longer distance routes, be a reluctance to willingly stand in the aisle ways. Some passengers still appear to think that standing is only safe in vestibule and door areas.
For (less seats bigger aisles) layouts to be a success, then passengers really have to be half expecting and willing to easily accept standing within the aisleways near to other seated passengers. If those passengers would rather have a bigger chance of a seat, be it possibly a cramped one then 3+2 is perhaps a better choice.
There is one other benefit of 3+2, which is that if you take it to be the case that a train feels crowded as soon as someone has to sit directly next to someone they are not travelling with, you can get 3 passengers per row rather than 2, as the middle seat acts as a very effective divider.
I have proposed before that it would be good to see 3+1 trialled in some parts of Standard, because that also has the same effect while retaining wide seats - groups of 6 are, off-peak, quite popular on LNR with families and small groups travelling together. Though being able to have a single seat in Standard may reduce the call for First Class.
Talking of which, I wonder what 1st layout is proposed for these units? Decent 2+1 and I'll happily cough up the LNR-Only 1st walk-up fares at their current rates (2+2 "First Class" with less comfortable seats and less legroom than Standard is a total sham and should not be allowed; if I had a 1st ticket on LNR at present on anything other than a 350/2 I would sit in Standard). Sadly, the only First Class worth paying for on LNR at the moment is the Class 319s, which have the best 1st in the fleet but don't operate on journeys where it's really worth bothering. Hopefully they will do what they should, which is one fewer seat across the width of the train than Standard.
Talking of 3+2, though, I think the East Anglia units look "least worst" in this regard - decent seats and seat back tables. So if they're the same as those they will be a step up from the /2s.