Well we already have one G-registered harp (G-RUKA) with more to come, according to reports. Not a big leap to add shamrocks really? And EI- registered aircraft have been based at UK airports for years too ...
Meanwhile - sacrilege, I know - I hope that Aer Lingus delays the launch of the new base at MAN until Summer '21. I'd expect them to fly alot of fresh air around during February to May which would get things off to a very bad start and undermine the long-term financials of the project. By Summer, there is a much improved chance that the innoculation programme and easing travel restrictions will facilitate a broader range of flying again. Early in the year, I can only foresee a debilitating labyrinth of restrictions and travel bans for discretionary Transatlantic business. Of course, perhaps they will take early season bookings 'just in case' and then consolidate them over DUB closer to the time? That early morning A320 still operates MAN-DUB most days. Connections available. Consolidating onto BA over LHR using the Shuttle would also be an option in the early months, this being a codeshared IAG initiative.
I see that the Canaries have just been cancelled again by HMG ... for the crucial Christmas / New Year trading period too. No light at the end of the tunnel for leisure air travel just yet. Sadly, it looks too soon for Transatlantic to resume in volume.