But, why stop at one licencing method? I find a maintenance plan a more friendly way especially since C2's tradition has been regular updates. For example: Pay a yearly maintenance, get updates. If you stop paying, you don't get upgrades but can use the last version you paid for. If you want to take up the maintenance again, it can be taken up again for the full price or some other price you deem fair.
Another approach is to award loyalty: For example, Unity subscribers have the option to own a perpetual license of Unity after two years. This also mitigates the problem of not being able to open your files later.
I like the loyalty idea. Hell I'd happily sign up for 5 years if it meant that after those 5 years I was guaranteed a perpetual license for the software at the state it was in when my rental ended.
Great suggestions. I'd love to hear Scirra's opinion on these. They were posted in several topics, but as far as I can recall, none of these got replies from Scirra, so I'm curious what's their opinion on these.