We all respect the effort that have done by NopCommerce team. I believe we all agree on that they deserve to get some money from the vendors BUT most of us disagree on the mechanism.
Some of vendors their sells seem very high such as Nop-Templates so they don't mind to pay that amount of money, but many of the vendors are not. I am telling you that having poor marketplace will affect all of vendors.
I suggest to have the following suggestion:
1- To have a one-time fee such as $60 per year. 2- To have 2 marketplace, Premium and Common market places. To have your plugin at premium, you need to pay, so customers know that Premium market place has the best plugins. Common market place is for plugins for vendor who doesn't need to pay any fees. NopCommerce can put a note that Premium marketplace has the best and trusted plugins.