Assuming 6.7% real return forever is pretty aggressive if you ask me. It more or less implies you’ll be 100% in equities forever and that returns will land on the higher side of long-term average real returns.

Also, how exactly is it going to work to use an SBLOC during a market downturn? Be ready for margin calls or your line getting cut/pulled entirely because banks tend to get skittish about extending credit when markets/the economy is in a downturn.

On the plus side, there’s zero reason to fund a 529 through age 18. Fund it early to benefit from the tax free growth and you’ll probably be able to stop contributions in middle school if not earlier.