There are 2 types of features that could be sold:
- useful features
 - useless features
Obviously, nobody will buy useless features. And for any useful feature players will say "hey, it makes game a lot easier, why do I have to pay for it? I want it for free."
The problem is that if we remove all useful features from premium, we can just change it to "Donate" button. With such approach even Wikipedia has to plea their users to donate every half a year, and we are far from their popularity and usefulness.
If the project won't earn any money, it will be closed. Both me and the coder are working on the normal job and support the game at the same time (right now - for free). It's very hard to handle this even for the short period of time, so if we will get less money than from ordinary job, there won't be any sense to support the game. "Donate" button won't even cover the hosting services. And we're not going to sell the ability just to upload a custom skin or something like this for wild money like some of our competitors do.