I understand your worries, but let me try to explain to hopefully give some more understanding. I speak totally on my own behalf; I'm not any kind of Joomla official, although I contributed in the architecture group whose working notes (nothing more, nothing less) you quote from.
Backwards compatibility is very high on Joomla's priority list
and we have very rigid rules for it. We don't break backwards compatibility within the 3.x series. We put a lot of effort in keeping that promise. That is already quite a challenge, for it might even mean that we officially support Joomla 3 functioning on php-versions that are now or in the future known as insecure. After the last version of Joomla 3 (which will be earliest somewhere over a year, but possibly even later) it will be supported for 2 more years!
So you can be sure of at least 3 more years of total backwards compatibility of Joomla
But the world changes, it even changes very fast, and we also want to be able to use new techniques and use some great software that is available but needs a higher PHP-version than what we promised to support. Inevitable there will be some point where backwards compatibility is not totally maintainable. Then it is time to migrate to a next major version. We use Semantic Versioning http://semver.org/
Given a version number MAJOR.MINOR.PATCH, increment the:
- MAJOR version when you make incompatible API changes,
- MINOR version when you add functionality in a backwards-compatible manner, and
- PATCH version when you make backwards-compatible bug fixes.
In your first quote from our minutes "No action required" means: we stick to semantic versioning, no new policy necessary. "Some effort will be made to allow J3 extensions to work with J4." means: we even do something extra, which is not obligated by semantic versioning. Because we care!
When the time inevitably comes for a new Major version, we must do all necessary backwards incompatible changes at that
moment, for it will take years from there before we can do that again.
But even within the inevitable backwards incompatible changes we are very careful:
- to not break anything without necessity
- to provide a good upgrade path and upgrade tools.
With every proposed change we also discuss how upgrades will be done. And still, daily, discussions about Joomla development end in shooting off good ideas because we cannot convince the others of the possibility of a smooth upgrade path; I can really tell from experience
We are developers ourselves and we know the pain of migrations like we had from 1.5 to higher as no other. Never again, we said. We do our very best to provide an upgrade to Joomla 4, also of extensions as smooth as possible! We are not the marketing department, but had some slogans during our meeting like "migration without frustration
- total backward compatibility is not realistic and even worsening Joomla in comparison with others who do offer newer possibilities.
- we try to make the transition as smooth as possible for everybody (integrators, developers etc).
Another thing: if you want to contribute to an even smoother transition: Joomla certainly need volunteers to help with this! Developers, integrators etc. How much time do you have available? What can be your contribution?