Many core layouts force the page layout to one of the five included with the core

[ericmorand]

Violation

Many core layouts force the page layout to one of the five included with the core.

Why it is a violation

This issue prevents developers to provide custom page layouts and remove the core ones without reviewing and extending every layouts provided by the core modules. This is a violation because layouts are provided by modules and module writers can't know by advance what page layouts will be available at runtime. Magento 2 implementers are expected to remove the five default page layouts and provide their own custom ones because the chance that the design they have to implement fits in one of these five page layouts are very slim.

This is a blatant violation of the principle of Separation of Concerns: layouts don't know anything about where and how they will be used, and they must not assume anything in that regard.