No one has ever said anything about older versions ever becoming unaccessible.
I'd better have Ashley to clarify that, it must be an official pronunciation from Scirra, not from the community devs trying to make conclusions. We must have a guarantee that it will work permanently at r388, and that all our old projects will be able to access the internal features to freeze any updates to the lates c3 stable on our side when this goes live.
Here's some quotes of the milestones:
Milestone 4: Construct will remove support for SDK v1 addons. The addons will no longer be loaded in the editor, and projects using them will fail to open and report that the addons are not supported and need updating. This will be at least 6 months after milestone 3 (and so at least 12 months after milestone 2).
Construct will ultimately drop support for the Addon SDK v1, so addon developers should consider starting updating their plugins and behaviors to use the Addon SDK v2.
skymen None of the quotes above indicate that what I state won't happen.
Ashley's comments about LTS.
It's infeasible to keep supporting one version forever. Eventually we will have to stop supporting it. As far as I'm aware nobody else in the industry supports LTS versions forever - everyone has some schedule of eventually retiring old LTS versions and introducing new LTS versions, sometimes with overlap between them. The question is what schedule is being proposed here
Ashley please clarify.