At the risk of swimming against the flow, for the 333s at least I'd prefer the ironing boards. The current seats are way to thick for the actual layout, and as a result many airline seats are seriously uncomfortable to squeeze your legs into. Plus ironing boards might free up a tiny bit more legroom in the 2x2 & 3x3 seats, and encourage a few more people to sit down rather than cram into the vestibules on the morning peaks when there are dozens of seats still available (for some reason on the Aire & Wharfe lines this is more common in the mornings, evening peaks see passengers using more or less every seat).
After all its not as if they will ever work regional or long distance services with Northern, the longest journeys they'll be making for now will be to Skipton & Doncaster at around 44 minutes for each, with the latter unlikely to see more than a handful of passengers using it for the full length.