We understand your idea on houses and all, but software is different. I would give you more credit if you compared it to a rent able Car or Power tools. First I think they are determined on their pricing model and will stick to it, irregardless of our voice. Usually small companies need a predictable / forecast-able annual revenue. Scirra will take this risk, from there they would assess whether to change from one-time payment or subscription model.
Look I totally get that and Scirra is in their right to put whatever licensing model or price they want on their product. I am just trying to explain why subscriptions don't feel nice spending money on.. especially now with all the competing products on the market.
Be it a house or a car - renting it out makes it unreliable and changes how and when you use it.
There are a lot of very good game engines that are completely free and make money from the services they offer to professionals. They charge you only when you turn out a huge profit. Those are the engines that real professionals actually use - Unreal and Unity3d!
You know what, that makes them accessible to people to learn - as there are no limitations imposed on the user to create a full game. No limitations on the development period, no limits on the size of the game
That is partly the reason for their success
The more you impose limitations- even to your loyal paying customer, the more you will see them leave for the other engines. This is a domino effect - the number of content created is less, fewer games to advertise the engine, fewer tutorials, less assets on the market. Believe it or not - the quality of a game engine hugely depends on it's community. It is not just the developer. Game engine devs such as Defold understand that very well and even invest huge amounts of money in advertising their free engine