We genuinely believe that there is a real chance of conquering 1⁄5 of the total cash market in the next decade, this has never been measured in a DeFi way, but we can approximate the value of this Market.
If we take World GDP and round it up to 90TUSD today, the Market Size looks as follows: 90TUSD GDP/5 = 18TUSD.
Then, let us take the concept of velocity described succinctly by the Federal Reserve Bank of St. Louis:
The velocity of money is the frequency at which one unit of currency is used to purchase domestically-produced goods and services within a given time period. In other words, it is the number of times one dollar is spent to buy goods and services per unit of time. If the velocity of money is increasing, then more transactions are occurring between individuals in an economy.
The velocity of money is calculated by dividing GDP for a certain period by the total money supply. For example, if the GDP is $20 trillion, but there are only $5 trillion worth of dollars available, then that money needs to turn over four times, or have a velocity of four, in order to meet demand in any given year. Currently, the velocity of the USD is a little north of 5. 
If we divide 18TUSD by five again, we would need 3.6TUSD of GAUs available to cover the demand of that Market.
Another measurement is the Wealth Market given by "The Global wealth report 2021" by Credit-Suisse. One-fifth of that Market is the astronomical amount of 83TUSD that the GAUGECASH needs to serve.