There are a couple of problems with this
- We don't exactly know where the new coastlines will be. Is all of the ice going to melt? As humid as it gets, the water in the atmosphere shouldn't make that much difference to the sea surface height, so this is all about ice.
- If all the ice does melt, there's some disagreement about when this would happen. The official forecast is something like a decimeter SSH rise by the end of the century. This is because climate scientists, as much as they make fun of financial analysts for doing this sort of thing, seem to favor a stable year-over-year rise in global average temperature.
- We won't get beaches right away. We'll have to suffer through possibly decades of extreme wetlands. Good for the mangrove farmers, bad for beach tennis. If you knew where the coastline would be when the ice was all gone and when that would happen, it wouldn't be sandy for another several decades.
- Climate change will cause crop failure and major disruptions in transportation and probably communications, as well as pandemics and surprise effects like these beach bacterial infections we have now and (pet theory alert) tsunamis. It seems unlikely our challenged democracy will survive, and we should end up in a more pronounced plutocracy, where the private army of some rich person will just take whatever property that rich person wants.