2 minor corrections

I want to comment on 2 statements which are not correct or at least confusing:
1. Statement "some changes to the system could not be reversed".
In principle, all changes in key user extensibility can be reverted. However, you have to do them in the right order. If there are dependencies to other objects, you first have to delete the dependencies. This is to protect key users from ending up with inconsistent objects.
And, in custom business objects, the tables are protected against incompatible changes (deletion of fields) to prevent data loss.
2. Statement "They [the key user objects] also generate objects with language version 2 (ABAP for Key Users) and are therefore not reusable with ABAP Cloud (language version 5)."
This is not completely correct the access is limited. But for example access to key user custom fields is 100% possible. Access to custom business object data is possible via an API, ... . The rules are described here in the documentation: https://help.sap.com/docs/SAP_S4HANA_CLOUD/0f69f8fb28ac4bf48d2b57b9637e81fa/3ccb50e724b045508fea8b2cf1774b2b.html#key-user-extensibility-and-developer-extensibility
I hope that this information helps. And again: apart from these small things, a very helpful blog.

Thank you Thomas, will add the session on monday in the sources area.

Nicely written

Thanks for the nice overview. If you are interested in key user tools, you may want to watch my Devtoberfest session What Software Developers Should Know About Key User Extensibility
What Software Developers Should Know About Key User Extensibility https://community.sap.com/t5/devtoberfest/what-software-developers-should-know-about-key-user-extensibility/ev-p/13806665
on upcoming Monday, Oct 14 at 8:00 AM CEST
I would be glad to see you there!