Within a single 10 year span, I would not count on the 400k doubling. Yes, the -average- return for equities(assuming) is around 10%/year for the S&P500(~7 or 8% after inflation), but that is smoothed out on 30 year time horizons. Within a single 10 year time span, well, it could be much higher or lower than that. FIRECalc shows possible 10 year values from 277k to 1.5mil, with an average of 733k(which I'm guessing is mean average, median appears to be closer to 600 something).
That said, if you're just spitballing hypotheticals, and the main aim is to accumulate a stash and then downshift to lower stress work and let time work for you while you enjoy yourself, than yeah your plan works.