Pretty much everyone that used the service after we made the fees optional decided to donate something, so as long as this continues we should generate more than enough to be highly profitable, especially with the increased usage that we expect after the above features are implemented.
If users are paying fees/donations on a voluntary basis that probably means they are happy with the service they received. If that continues then your customers will continue to have a fee-free service.
The anonymity set shows 240 user deposits. If this number is effectively the grand total of mixes to date, it serves a purpose when it is related to transparency however it can be used by your competitors to entice customers to use their service under the (true or false) guise of them mixing in the greater numbers than Whirlwind. Overall, is it a wise move to do that?
Of course it could also happen that usage increases, but everyone will donate 0 and in that case we will have to implement a minimum fee again, but we doubt that will be the case. And as we said before we will run the platform with 0 fees for at least 3 months before deciding if it is in fact viable or not.
It will be interesting to see the format you are operating after 3 months.