Membership of a global alliance is "overkill" for an airline such as Aer Lingus. They decided that the costs outweighed the benefits, and left in 2007 after less than 7 years of membership.

Aer Lingus has partnerships with the airlines for which it makes sense for them to partner with - not all of whom are oneworld members, by the way (UA/B6/AC) so there really is no reason for Aer Lingus to join oneworld. They're already in the oneworld immunised transatlantic joint-venture, in case you didn't know, so that's probably as much oneworld as Aer Lingus actually needs.

Nobody has been able to articulate the strong business case for EI rejoining. You've mentioned aspects such as lounge access and other concerns from the viewpoint of AA status holders - but those alone are not compelling business reasons for EI. Aer Lingus manages to fill its planes even without the benefit of having oneworld status holders deigning to fly EI just because their status benefits are observed. Aer Lingus has looked at this several times over the years since they left oneworld, and the business case for re-joining simply doesn't stack up. The topics you've mentioned - access to the AAdmirals Club (which will likely be where business class ticket holders and EI status members in economy will be accommodated) and the "plight" of BNA-based pAAsengers is not going to swing the decision for EI. (EI has been owned by IAG - the parent of BA and Iberia amongst others - for almost 10 years, and there still is no full reciprocal recognition between BA and EI of each other's elites, despite the fact tha the two airlines have always had a close working relationship, even before they were both in the IAG family. So please do NOT make the mistake that EI is chomping at the bit to to throw open the doors of recognition to all oneworld status holders, when they still don't do so for BA, the airline with whom they historically have transferred by far the greatest number of passengers) Neither will the mere fact of BNA joining as the 22nd (or is it 23rd?) North American destination be the "clincher" that means EI wants to be a oneworld member again.

(Besides, AA status holders who want access can surely instead book the ticket from AA under the AA codeshare number - rather than directly from EI under the native EI flightcodes - and have access to the AAdmirals club that way - right?)

Anyways, there's a thread for that kind of speculation so please take any further thoughts, comments or queries to that thread - but the short answer is, no - not really.

Aer Lingus possibly fully joining Oneworld in Q2 2025