I've always had a soft spot for Venus. The floating city idea is not my favourite, perhaps for research there could be applications. A monumental breakthrough in carbon sequestration, in method and cost might do it for Venus though. But I mean monumental. Back of the envelope calculations say there's about 460 Quadrillion metric tonne of CO2. Sooo, maybe at a cost 1c per metric tonne we could get it done with a current day cost of 4.6 Quadrillion US Dollars or so. Or all the worlds GDP for about 50 years. But that assumes that there would be no benefits from doing that. Could be other applications from the byproducts being sold.