No, they are not bidding against London for a Worldcon. This is a much better idea.
James Shields was this year’s GUFF delegate. As such he got to visit the New Zealand Natcon as well as Aussiecon 4. Inspired by how well that worked, James came up with the idea of having a convention in Dublin a week after the (presumed) London Worldcon. After all, lots of Americans will be coming over for Worldcon, and we all know how Americans love to visit Ireland. James is bidding to be a Eurocon as well. Pre-supports are only €5. Kevin and I have already joined. More details here.