Sea walls built to protect beachside housing tend to destroy the beaches, which then can be maintained only by artificially replenishing them.

A few decades from now, with sea level rising ever faster and various disasters striking, no region will be able to afford to sustain beaches artificially; rich people will do it in private enclaves.

I am no expert, but I suspect that the natural process that creates new beaches may be too slow to keep up with the speed of the rise as it will be a few decades from now. The process may not get a chance to work again until hundreds of years from now, when the Antarctic and Greenland ice caps have melted and sea level is a 100 or 200 meters higher.