My two cents...
First off, I would like to see some more links, coastal studies, that sort of thing. Like about sea level and coastal erosion. What I'm guessing we'll see is that sea level will continue rising slowly, but storm floods and wave levels will rise relatively faster...
"Heights of storm waves off the Oregon and Washington coast have measured as much as 8 feet higher than 25 years ago. Such waves deliver 65% more force when they come ashore."
http://www.ecy.wa.gov/climatechange/ris ... l_more.htm
Yes, I know this study refers to Washington state and not DC, but the point is that the change in wave height and energy delivered to beaches may sneak up like EROI is to Peak Oil. Massive erosion and short term flooding may hit way before long term flooding from a permanent rise in ocean levels.
Second, if the US dissolves as the Soviet Union did after collapse. Southern and Northern states may be separate countries, further affecting where the capital will be in the next x many years...
"The multiplication force of technology on cognitive differences is massive." -Jordan Peterson