The 777-9 will be too wide for the current B/E Diamond LH currently uses, unless they go for the 2-3-2 config they currently have on the 744 main deck
Considering the 777-9 will arrive with LH sometime in 2020-22, it sounds about right: the current seat will be 8-10 years old and written off. IAG also announced that they will have common widebody cabins across Aer Lingus, Iberia and BA, so this is a bit of a me-too.