I have yet to see these disasters you are talking about.
We see them - desperate customers with ruined projects come and beg us for help. Sometimes the addon developer responsible has left the community, and there's nobody left to help them.
Many addons continue working for years without any issues.
As I said before, these could all permanently break with any release. The main reason it hasn't happened already is sheer luck. I expect our luck will not last forever, especially as other addons can and do break on a fairly regular basis.
nobody blames you when this happens
They sure do. If someone's project works in r300 and breaks in r301, they contact us, tell us we broke their project, and whatever we did in r301 we should revert so their project keeps working. Trying to explain these issues of encapsulation to people is often fruitless as most customers don't care and often it sounds to them like we're just pointing the finger at someone else and shirking responsibility. It's a real nightmare for us to deal with and is continually happening in the background, unbeknown to most addon developers, often including the addon developers responsible for the problem.
To the others who have responded: I do appreciate your feedback; I am keenly aware of the value addon developers bring to the community; I greatly regret that we are adding more work for them to do. However an API with encapsulation is the industry standard. No other serious tools allow addons such unfettered access to engine internals, precisely because it is an unprofessional and reckless way to develop software that most people in the industry understand will end in disaster. Part of the project of the Addon SDK v2 is to increase the existing API surface to make sure it's more capable and do so in a way that is reliable in the long-term. Where possible, we are also making some addon's features built-in, which also removes the need for the addon to be ported. For example the next release includes a 'Reset' action for event variables, so that it is no longer necessary to use an addon to do that. We will be continuing this to make the best effort possible to smooth the transition and make sure any key features are implemented in Construct itself.
I know we're asking a lot here. But if we don't act, in extremis this could turn in to an existential problem for Construct, ending in development hell where every update breaks loads of projects and we are in effect no longer able to improve Construct any further; ultimately that can lead to the failure of the product on the market. This has happened to other products before and, as things stand, could easily happen to us in future. I am doing my best to explain that this is a real, active risk, there are signs of it happening already, it's likely to get worse, and it warrants serious action to rectify. I am asking addon developers and customers alike to make a good faith effort to take seriously the risks we are facing, and I am asking for others to co-operate as we go through what will unfortunately be a disruptive but necessary process. We have to think on a 5-10 year time scale, and we need to go through this to be in a better place in future.