Very odd/confusing development.
a) Why announce so far ahead of time? People will have forgotten this announcement by the time service actually starts.
b) Service to Madrid will be head-to-head with IB, a core OW carrier (with the networking benefits of OW, which are set to expand dramatically) and also anational "flag carrier". Tough sell.
c) Aer Lingus has name recognition in Britain, plus the British regions are in general absymally served in terms of direct TA flights. Consequently it would appear to have been more natural for EI to have gone after MAN-XXX or GLA-XXX traffic. [Though of course they could try and serve these via DUB, which they have never really pursued in any depth.]
d) Who will think of EI as other than an oddity when wanting to travel from US to Spain or vice versa?