If I pay for your product, I want to own it. I don't care if you keep adding "useful" features like emoji-integration, I'm not paying multiple times for the same product, especially if I don't even get to own it. If I truly wanted your little updates, then let's negotiate a 1-TIME fee to incorporate them into the product I own.
Now, if you are selling a service that requires continuous work to be done as a function of time, then I shall pay a continuous payment as a function of time. Example: servers, VPN, VPC. However, your constantly adding of "features" to a product does NOT go toward keeping the base product, that I purchased and own, running. You spent a fixed amount of man hours making the product, so I pay a fixed amount of money. If you spend an additional fixed number of man-hours on new features, I shall consider paying another fixed amount of money for them.
Now, if you are selling a service that requires continuous work to be done as a function of time, then I shall pay a continuous payment as a function of time. Example: servers, VPN, VPC. However, your constantly adding of "features" to a product does NOT go toward keeping the base product, that I purchased and own, running. You spent a fixed amount of man hours making the product, so I pay a fixed amount of money. If you spend an additional fixed number of man-hours on new features, I shall consider paying another fixed amount of money for them.