I don’t understand what is the unlikely thing to happen in the scenario described. If you’re talking about striking millions in startup exit/IPO money, I def agree with you it’s unlikely.
Plenty of engineers hit their cap at L5 or thereabouts (I'm sure if you look at the distribution of levels at your local bigco you'll see there's a sharp decline in numbers at some point), and not everyone is going to be part of a DINK engineering power couple.