Versus their immediate predecessors, the consumer Blackwell GPUs are increasing performance in AI first; followed by ray tracing; general FP32 shader performance and texture fill rate a distant third; and pixel fill rate very little. Elite: Dangerous has no way to leverage the AI or ray tracing capabilities, which leaves a moderate FP32 increase.
Problem is that even with graphical mods and custom settings, the only place to really spend GPU performance, at the top-end, is trying to push enough raw pixels to make the AA situation less dire. This new generation of cards is ill-suited for that because the ROP count and clock speeds aren't increasing meaningfully. The extra memory bandwidth of the 5090 will help a bit vs. the 4090, but even that won't be huge.
The 5080 will almost certainly be somewhat slower than the 4090 in ED(O), though the 5090 should become be fastest by some margin.