There reaches a point when the fundamental design principle of something cannot be overcome with software or other mitigations. The basic science is that salt water and electricity do not mix - the fact that modern trains have equipment designed to conduct electricity all over the place - on the roof, between vehicles, under the floor - means they are going to mix with sea water less readily than something more mechanical. I was surprised to see Hitachi selling their products as 'Dawlish proof' - I wouldn't haven taken that PR risk even if I were convinced it were true.
Given where rolling stock design has gone (and is going) with hybrid, battery and bi-mode rolling stock all based on electrically driven traction motors and other equipment, I'm struggling to see how future designs can best mitigate the 'Dawlish Sea Wall' problem - to me the ultimate solution is actually in the railway infrastructure, whether that's covering it over at the worst points or further work on wave return walls.
More durable diesel-only rolling stock is all very well, but it has no future on the railway.