> So you're looking at about a 10 year lag from best consumer GPUs to a GPU with similar performance to a modern phone.

Two competing viewpoints to this:

1) It is getting harder to make the same performance gains, so maybe that 10 year window grows to 15 or 20.

> Put another way, their investment is going to be worthless in 10-15 yyears, absolute max.

2) The value of a GPU is not its flops relative to to other GPUs. Its value is it's output minus it's cost. If the value of its output is stable, or grows, it doesn't really matter if its efficiency relative to the latest and greatest diminishes.