I'm planning on releasing some tools and I would like to be able to charge a monthly subscription amount for this. There are other sites (github f.ex.) that can do this, but I don't want to put all eggs in one basket.

Is this something feasible to add in the future? I know it entails additional complexity (storing encrypted billing information, controlling the date billed, etc.)

How would you actually enforce it once they've downloaded the software?

MMO with account. The way I'm solving it with github is you add your github account name to your account in my game and github has a API to ask who is sponsoring you and for how much so I can verify everyone is paying.