Really interesting, thanks Paul!
This topic could provide a wealth of information and illustrations as its been my experience that in contrast to other Cities in the Eighteenth and particularly Nineteenth Centuries, most proposals for Dublin remained on the drawing board.
I know you have already alluded to some of them on Archiseek, such as the various Bridges proposed for the Liffey, the Crescents at both Dublin Castle and the Customs House, the extension of O'Connell Street, the Cathedral in the Capel Street area, and the various Abercrombie transport proposals.
Just off the top of my head, I've heard of other rather audacious proposals such as a ship canal from Dun Laoghaire to Grand Canal Dock, a massive enclosed military fort in what is now the Mount Street/Ballsbridge area or the mile long sea wall stretching from Sandycove to enclose a large sheltered anchorage centered on Bullock Harbour.
I'm sure there are many others. Personally, I've always heard that immediately prior to the Act of Union in 1800 the Wide Streets Commissioners had very grandiose masterplans drawn up which became just another victim of the loss of trade and revenue when Government shifted to London, I've never seen anything concrete though.