Wealth Distribution of the Super-Rich
Some thoughts: 


accurate prediction seems ambitious without empirical data; 
many people have negative or zero net wealth; 
a continuous distribution could lead to oddities; 
the world may have a finite total wealth and so a finite average wealth thus excluding some distribution shapes such as Pareto distribution with $\alpha \le 1$


But you could certainly develop a model, even if it would be wrong.  For example, let's try:


A Pareto distribution with shape parameter $\alpha$ and scaling parameter $x_{\min}$
The application of the Pareto 80-20 principle, so $\alpha=\log_4(5) \approx 1.160964$
A total global wealth of perhaps of the order of $\$ 250$ trillion and a global population of about $7.4$ billion, giving an average wealth $\mu$ of about $\$33784$ and $x_{\min}=\mu\frac{\alpha-1}{\alpha}$ would be about $\$4684$ (looks rather high to me, but $x_{\min}$ is really a scaling factor and should not be taken too seriously)
A Gini coefficient of $\frac{1}{2\alpha-1}$ would be about $0.76$
The top $1\%$ (so $74$ million people) would have over $x_{\min} / 0.01^{1/\alpha}$ each, so here about $\$250,000$ 
a person with wealth $w$ would be at the $\left(\frac{x_{\min}}{w}\right)^{\alpha}$ quantile measured from the top  


Since this probably does not fit reality, you can then start adjusting it if you want: for example you can get closer to a Gini coefficient of $1$ if you reduce $\alpha$ towards $1$ from above, and this would also lower $x_{\min}$.   If you use a Gini coefficient of $G$, that would make $\alpha=\frac{G+1}{2G}$ and $x_{\min}=\mu\frac{1-G}{1+G}$ so the person with wealth $w$ could be at the $\left(\frac{\mu(1-G)}{w(1+G)}\right)^{(G+1)/(2G)}$ quantile, measured from the top.

Or you could decide to give a certain share of the population a wealth of zero.  If the rest keep the same $\alpha$ on a (now zero-inflated) Pareto distribution this will increase $x_{\min}$ for the rest while also increasing the Gini coefficient overall.

Or you could look for empirical information on the actual wealth distribution and then try to fit a curve to that.  Or perhaps look at global income distribution instead, which has not had a particularly simple function in the past.