I like that model, too, but at least for something like 1Password I can see two issues. You'll have people using older versions with possible security vulnerabilities. If you're using hosted passwords you have to deal with dealing with multiple versions of the client indefinitely (although, you'll probably have to deal with a bit of that anyway)
When you include the hosting service, having a subscription (since you're providing an ongoing service) makes perfect sense. In this case, so does also forcing the current version.
I agree that subscriptions make perfect sense for services (because servers, support, etc. cost money on a monthly basis), but the trend seems to be to create an arbitrary reliance on a hosted service as a way to justify subscriptions. Luckily 1Password hasn't totally gone that way yet, since they still offer standalone licenses for local vaults, but I feel like it's the direction they're going.
