It's not particularly tempting to A/B test seats which will cost you $500k per aircraft to install. Plus you can't conduct real world tests on equipment which doesn't have the relevant certifications.
People also don't like to be surprised by their brand, at least in non-trivial ways. I'd predict constant A/B testing of disruptive ideas (such as new seating arrangements or radically boarding schemes) would end up damaging the brand and customer retention.
They could do focus groups though. Build a few different seating arrangements, pay people to sit in them for a couple hours, and collect their thoughts afterwards.
