Hello, have you considered the option of paying for updates ?.
The user would pay 100 USD for one year of updates, when the year elapses the user no longer receives new updates until a new payment is made.
The user gets C3 with the only limitation that he can not receive updates but he can continue editing his projects.
A connection is still required at least every week to avoid piracy problems.
To me (and I think for many more users) this form seems satisfactory and I would acquire C3, I would probably update it too often.