Agree we need some of this in the core, so good call.
Regarding the canonical; this should be, and can be, automated. Mount points and show contents of this page can be automated. A big challenge lies in language fallbacks, since there are many options to consider.
OG tags and Twitter cards; will that affect SEO, or just influence the performance of your links on social media? Social Media is not equal to SEO, so if there is no effect in SEO, I would put them in separate extension.
I personally would put this in a separate core extension. There are many installations who do not need this, like intranets. The website developer should be in charge to define if this functionality should be used.
@richardhaeser; you do have a customer where the page title is in the page