That's effectively paying a massive premium for liquidity you almost certainly won't need.It’s a bit like having an emergency fund that’s equal to the amount outstanding on your mortgage; I wouldn’t advocate clearing the mortgage.
IMO paying down a mortgage ahead of schedule is the best college funding plan.
I might take a different view if we had a tax-advantaged saving scheme for college expenses (like 529 plans in the US). But unfortunately we don't have anything like that here.